Fixes runtimes caused by dreamluau's absence (#86171)

## About The Pull Request

Currently, if dreamluau is absent (which it might be on linux instances
that don't automatically download it), every `call_ext` call runtimes,
crashing the calling proc. This fixes that by using a flag that skips
calling `call_ext` if unset.

## Why It's Good For The Game

Apparently this could really bork the garbage collection subsystem, so
fixing it is a really good idea.

## Changelog

Does this even count as a player-facing change?

code/modules/admin/verbs/lua/lua_state.dm

@@ -41,7 +41,10 @@ GLOBAL_PROTECT(lua_state_stack)
 		return
 	display_name = _name
 	internal_id = DREAMLUAU_NEW_STATE()
-	if(!isnum(internal_id))
+	if(isnull(internal_id))
+		stack_trace("dreamluau is not loaded")
+		qdel(src)
+	else if(!isnum(internal_id))
 		stack_trace(internal_id)
 		qdel(src)