fix(nui): use correct queue key for frameCall messages

[gtolontop]

Goal of this PR

Fix NUI messages being silently lost when sent before the UI has finished loading. The message queue was using the wrong key for frameCall messages, causing TriggerLoadEnd to never find and flush them.

How is this PR achieving the goal

The g_processMessageQueue uses frame names as keys, and TriggerLoadEnd flushes queued messages by frame name. However, the original code used argumentList->GetString(0) as the queue key for all non-rootCall messages — this is the message type (e.g. "frameCall"), not the frame name.

For frameCall messages created via PostJSEvent("frameCall", { frame, jsonData }), the frame name is at index 1, not index 0. The fix correctly extracts the frame name from the argument list based on the message type:

• frameCall: uses argumentList->GetString(1) (the frame name)
• rootCall: uses "__root"
• Other types: uses argumentList->GetString(0) (unchanged behavior)

This PR applies to the following area(s)

FiveM and RedM NUI core (nui-core)

Successfully tested on

• Verified that frameCall messages sent before UI load are correctly queued under the frame name and flushed by TriggerLoadEnd
• Verified that rootCall messages continue to queue under "__root" as before
• No regression in normal message delivery when the browser is already loaded

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.

Fixes issues

Fixes #3847