[MIRROR] fix some runtimes and an overlay overflow (#8210)

Co-authored-by: Kashargul <144968721+Kashargul@users.noreply.github.com>

code/modules/examine/descriptions/guns.dm

@@ -18,6 +18,8 @@
 		else
 			ammo = projectile_gun.contents[1]
 		P = ammo.BB
+	if(!P)
+		return "no"
 	switch(P.damage)
 		if(0)
 			return "no"
@@ -57,6 +59,8 @@
 		else
 			ammo = projectile_gun.contents[1]
 		P = ammo.BB
+	if(!P)
+		return "no"
 	switch(P.armor_penetration)
 		if(0)
 			return "cannot pierce armor"
@@ -149,4 +153,4 @@
 	if(reach > 1)
 		weapon_stats += "\nIt can attack targets up to [reach] tiles away, and can attack over certain objects."
 
-	return weapon_stats
+	return weapon_stats