Fixes parallax runtimes when your eye is not a mob (#71072)

## About The Pull Request

Also properly supports passing no input into the update proc

code/_onclick/hud/hud.dm

@@ -173,7 +173,7 @@ GLOBAL_LIST_INIT(available_ui_styles, list(
 
 /datum/hud/proc/eye_z_changed(atom/eye)
 	SIGNAL_HANDLER
-	update_parallax_pref(eye) // If your eye changes z level, so should your parallax prefs
+	update_parallax_pref() // If your eye changes z level, so should your parallax prefs
 	var/turf/eye_turf = get_turf(eye)
 	var/new_offset = GET_TURF_PLANE_OFFSET(eye_turf)
 	if(current_plane_offset == new_offset)

code/_onclick/hud/parallax.dm

@@ -83,11 +83,12 @@
 			return FALSE
 
 /datum/hud/proc/update_parallax_pref(mob/viewmob)
-	if(!viewmob.client)
+	var/mob/screen_mob = viewmob || mymob
+	if(!screen_mob.client)
 		return
-	remove_parallax(viewmob)
-	create_parallax(viewmob)
-	update_parallax(viewmob)
+	remove_parallax(screen_mob)
+	create_parallax(screen_mob)
+	update_parallax(screen_mob)
 
 // This sets which way the current shuttle is moving (returns true if the shuttle has stopped moving so the caller can append their animation)
 /datum/hud/proc/set_parallax_movedir(new_parallax_movedir = 0, skip_windups, mob/viewmob)