Fix AttributeError caused by unknown languages

What does this merge request do and why?

We are seeing an increased error rate related to 'NoneType' object has no attribute 'name'.

Traceback (most recent call last):
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/anyio/streams/memory.py", line 98, in receive
    return self.receive_nowait()
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/anyio/streams/memory.py", line 93, in receive_nowait
    raise WouldBlock
anyio.WouldBlock

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 43, in call_next
    message = await recv_stream.receive()
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/anyio/streams/memory.py", line 118, in receive
    raise EndOfStream
anyio.EndOfStream

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/app/ai_gateway/api/middleware.py", line 107, in dispatch
    response = await call_next(request)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 46, in call_next
    raise app_exc
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 36, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/authentication.py", line 48, in __call__
    await self.app(scope, receive, send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 68, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/app/ai_gateway/api/middleware.py", line 274, in dispatch
    return await call_next(request)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 46, in call_next
    raise app_exc
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/middleware/base.py", line 36, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/exceptions.py", line 93, in __call__
    raise exc
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/exceptions.py", line 82, in __call__
    await self.app(scope, receive, sender)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/routing.py", line 670, in __call__
    await route.handle(scope, receive, send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/routing.py", line 266, in handle
    await self.app(scope, receive, send)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/starlette/routing.py", line 65, in app
    response = await func(request)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/fastapi/routing.py", line 231, in app
    raw_response = await run_endpoint_function(
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/fastapi/routing.py", line 160, in run_endpoint_function
    return await dependant.call(**values)
  File "/opt/venv/ai-gateway-9TtSrW0h-py3.9/lib/python3.9/site-packages/dependency_injector/wiring.py", line 994, in _patched
    return await _async_inject(
  File "src/dependency_injector/_cwiring.pyx", line 66, in _async_inject
  File "/app/ai_gateway/api/v2/endpoints/code.py", line 117, in completions
    suggestion = await code_completions(
  File "/app/ai_gateway/code_suggestions/processing/base.py", line 79, in generate
    return await self._generate(
  File "/app/ai_gateway/code_suggestions/processing/completions.py", line 214, in _generate
    watch_container.register_lang(lang_id, editor_lang)
  File "/app/ai_gateway/instrumentators/base.py", line 119, in register_lang
    {"lang": lang_id.name.lower(), "editor_lang": editor_lang}
AttributeError: 'NoneType' object has no attribute 'name'

https://log.gprd.gitlab.net/app/discover#/doc/8cd9c4c0-f0a7-11ed-a017-0d32180b1390/pubsub-mlops-inf-gprd-000022?id=wnn3-IoBouij7zpEyolK

This bug was introduced by !409 (merged)

How to set up and validate locally

1. Ensure a local Docker image built successfully.

   docker buildx build --platform linux/amd64 \
     -t ai-gateway:test .

2. Run a local service on Docker.

   docker run --platform linux/amd64 --rm \
     -p 5052:5052 \
     -e AUTH_BYPASS_EXTERNAL=true \
     -v $PWD:/app -it ai-gateway:test

3. Send a cURL request to the /v2/completions endpoint with an unsupported file extension.

   $ curl --request POST \
     --url http://codesuggestions.gdk.test:5052/v2/completions \
     --header 'Content-Type: application/json' \
     --header 'X-Gitlab-Authentication-Type: oidc' \
     --header 'authorization: Bearer jwt \
     --data '{
     "prompt_version": 1,
     "project_path": "gitlab-org/gitlab",
     "project_id": 278964,
     "current_file": {
       "file_name": "main.vue",
       "content_above_cursor": "# write an awesome function",
       "content_below_cursor": ""
     }
   }'

4. Observer the error in the log

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.