Fix med_hud_set_health runtime for xenomorphs (#4951)

# About the pull request
Fixes below


![image](https://github.com/cmss13-devs/cmss13/assets/41448081/ef8b8ae6-9e23-420e-acbe-24ddf035b7e5)

Same rationale as #4948

code/datums/mob_hud.dm

@@ -283,6 +283,12 @@ var/list/datum/mob_hud/huds = list(
 	return
 
 /mob/living/carbon/xenomorph/med_hud_set_health()
+	if(QDELETED(src))
+		return
+
+	if(!(HEALTH_HUD_XENO in hud_list))
+		CRASH("hud_list lacks HEALTH_HUD_XENO despite not being deleted in med_hud_set_health()")
+
 	var/image/holder = hud_list[HEALTH_HUD_XENO]
 
 	var/health_hud_type = "xenohealth"