Avoid commit when snippet file_name and content are not present

What does this MR do?

If the file_name and content params are not present inside the attributes we pass to the snippet update service, there is no need to actually perform a commit action.

Closes #214692 (closed) and https://gitlab.com/gitlab-org/gitlab/-/issues/214683

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content