fix(streaming/five): add missing lock in GetStreamingIndexForLocalHashKey

[ShamZy9]

Goal of this PR

Fix a data race in streaming::GetStreamingIndexForLocalHashKey.

The function reads g_streamingHashStoresToIndices without acquiring g_streamingMapMutex, while AddStreamingFileWrap writes to the same map under a std::unique_lock. The three sibling accessors (GetStreamingIndexForName, GetStreamingNameForIndex, GetStreamingBaseNameForHash) all correctly take a std::shared_lock; this one was missing it.

A concurrent find() on a std::map while another thread inserts (rebalancing the tree) is undefined behavior and can cause intermittent crashes/corruption while custom streaming assets are being registered.

How is this PR achieving the goal

Acquire std::shared_lock _(g_streamingMapMutex); at the top of the function, matching the other accessors in the same file.

This PR applies to the following area(s)

FiveM

Successfully tested on

Game builds: n/a (adds a missing lock, no functional change)

Platforms: Windows

Checklist

• Code compiles and has been tested successfully.
• Code explains itself well and/or is documented.
• My commit message explains what the changes do and what they are for.
• No extra compilation warnings are added by these changes.