Fixes DVIEW runtimes in preferences. (#490)

code/__HELPERS/unsorted.dm

@@ -1315,6 +1315,8 @@ GLOBAL_DATUM_INIT(dview_mob, /mob/dview, new)
 	GLOB.dview_mob.see_invisible = invis_flags; \
 	for(type in view(range, GLOB.dview_mob))
 
+#define FOR_DVIEW_END GLOB.dview_mob.loc = null
+
 //can a window be here, or is there a window blocking it?
 /proc/valid_window_location(turf/T, dir_to_check)
 	if(!T)

code/game/machinery/dance_machine.dm

@@ -232,6 +232,7 @@
 			spotlights+=L
 			continue
 		continue
+	FOR_DVIEW_END
 
 /obj/machinery/disco/proc/hierofunk()
 	for(var/i in 1 to 10)

code/modules/lighting/lighting_source.dm

@@ -221,7 +221,7 @@
 
 		LAZYADD(T.affecting_lights, src)
 		affecting_turfs    += T
-
+	FOR_DVIEW_END
 	update_gen++
 
 /datum/light_source/proc/remove_lum()
@@ -262,6 +262,7 @@
 			C = thing
 			corners[C] = 0
 		turfs += T
+	FOR_DVIEW_END
 
 	var/list/L = turfs - affecting_turfs // New turfs, add us to the affecting lights of them.
 	affecting_turfs += L