tweak(scripting/lua): speed up lua event serialization.

[icy4471]

If there are no event handlers for the event, there is no need to unpack or set the source as they will never be used.

Goal of this PR

Significantly speeds up event serialization when there are no handlers available.

How is this PR achieving the goal

By returning early when there are no event handlers available.

This PR applies to the following area(s)

FiveM, ScRT: Lua

Successfully tested on

Game builds: b3095

Platforms: Windows, Linux

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

[thelindat]

Worth noting that this function is only triggered in functions which have registered the event previously, so this only helps with removed events. Possibly worth being able to remove resources from the event registry altogether?

[AvarianKnight]

Another thing to note here is msgpack_unpack should be called after the net checks.