Verify that only one of each callback type exists per map

Fixes #1213

constants/map_setup_constants.asm

@@ -22,6 +22,7 @@ DEF NUM_MAPSETUP_SCRIPTS EQU const_value - $f1
 	const MAPCALLBACK_CMDQUEUE
 	const MAPCALLBACK_SPRITES
 	const MAPCALLBACK_NEWMAP
+DEF NUM_MAPCALLBACK_TYPES EQU const_value - 1
 
 ; see data/maps/setup_script_pointers.asm
 DEF MAPSETUPSCRIPT_HAS_PARAM_F EQU 7

macros/scripts/maps.asm

@@ -39,11 +39,17 @@ MACRO def_callbacks
 	REDEF _NUM_CALLBACKS EQUS "_NUM_CALLBACKS_\@"
 	db {_NUM_CALLBACKS}
 	DEF {_NUM_CALLBACKS} = 0
+	for x, 1, NUM_MAPCALLBACK_TYPES + 1
+		DEF map_callback_{d:x} = 0
+	endr
 ENDM
 
 MACRO callback
 ;\1: type: a MAPCALLBACK_* constant
 ;\2: script pointer
+	DEF x = \1
+	assert !map_callback_{d:x}, "Already defined a `callback \1` for this map"
+	DEF map_callback_{d:x} = 1
 	dbw \1, \2
 	DEF {_NUM_CALLBACKS} += 1
 ENDM