Prevents TGUI crash when slime tries to feed with 0 valid targets (#28031)

* Prevents TGUI Crush when 0 targets was found.

* !

Co-authored-by: Contrabang <91113370+Contrabang@users.noreply.github.com>
Signed-off-by: Drsmail <60036448+Drsmail@users.noreply.github.com>

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Signed-off-by: Drsmail <60036448+Drsmail@users.noreply.github.com>
Co-authored-by: Contrabang <91113370+Contrabang@users.noreply.github.com>

code/modules/mob/living/simple_animal/slime/slime_powers.dm

@@ -29,6 +29,10 @@
 		if(C!=src && Adjacent(C))
 			choices += C
 
+	if(!length(choices))
+		to_chat(src, "<span class='warning'>No subjects nearby to feed on!</span>")
+		return
+
 	var/mob/living/M = tgui_input_list(src, "Who do you wish to feed on?", "Feeding Selection", choices)
 	if(!M)
 		return FALSE