Reorder snippet before action in controller

What does this MR do?

In the former code, we call the access checker before checking if the feature flag was enabled. That is a wrong behavior because we don't even need to check those unless the feature flag version_snippets is enabled.

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