Fix for queen eye runtime. (#3549)

# About the pull request

Followup to #3477.

# Explain why it's good for the game


![image](https://github.com/cmss13-devs/cmss13/assets/4447185/18230244-ce64-408d-9da0-43413a758134)


# Changelog
:cl:
fix: Queen Eye no longer repeatedly throws runtime errors.
/:cl:

code/modules/mob/living/carbon/xenomorph/XenoOverwatch.dm

@@ -71,10 +71,10 @@
 
 		SEND_SIGNAL(src, COMSIG_XENO_STOP_OVERWATCH, oldXeno)
 		UnregisterSignal(src, COMSIG_MOB_MOVE_OR_LOOK)
-		UnregisterSignal(oldXeno, COMSIG_PARENT_QDELETING)
 
 		if(oldXeno)
 			to_chat(src, SPAN_XENOWARNING("You stop watching [oldXeno]."))
+			UnregisterSignal(oldXeno, COMSIG_PARENT_QDELETING)
 			if(!QDELETED(oldXeno))
 				oldXeno.hud_set_queen_overwatch()
 	else