Minor vampire power changes (#3396)

-fix thrall not checking if it could be used on the victim
-antags and special characters should be immune to vampire mind control powers

code/game/gamemodes/vampire/vampire_helpers.dm

@@ -94,6 +94,10 @@
 			to_chat(src, "<span class='warning'>You lack the power interact with mechanical constructs.</span>")
 		return 0
 
+	if(is_special_character(T) && (!(T.mind.vampire.status & VAMP_ISTHRALL)))
+		user << "<span class='warning'>\The [T]'s mind is too strong to be affected by our powers!</span>"
+		return 0
+
 	if (account_loyalty_implant)
 		for (var/obj/item/weapon/implant/loyalty/I in T)
 			if (I.implanted)

code/game/gamemodes/vampire/vampire_powers.dm

@@ -657,6 +657,9 @@
 		to_chat(src, "<span class='warning'>[T] is not a creature you can enthrall.</span>")
 		return
 
+	if (!vampire_can_affect_target(T, 1, 1))
+		return
+
 	if (!T.client || !T.mind)
 		to_chat(src, "<span class='warning'>[T]'s mind is empty and useless. They cannot be forced into a blood bond.</span>")
 		return