Zoekt search returns 400 http status code for some searches
## Summary
some zoekt searches are generating 400 http response codes from the zoekt web server
## Steps to reproduce
Unknown
## What is the current *bug* behavior?
<!-- Describe what actually happens. -->
## What is the expected *correct* behavior?
<!-- Describe what you should see instead. -->
## Relevant logs and/or screenshots
kibana for zoekt 400 errors from webserver side: https://log.gprd.gitlab.net/app/r/s/pMr4z
kibana (internal) for zoekt client 400 errors: https://log.gprd.gitlab.net/app/r/s/Fw1Hs
```
{"Error":"error parsing regexp: missing argument to repetition operator: `*`"}
```
## Possible fixes
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issue