Fixes monkey cube Dupe Glitch

fixes https://github.com/tgstation/-tg-station/issues/14667

Adds some consistency, allowing monkeys to be drag dropped onto the
monkey recycler, like they are with the disposals chutes.

Prevents grabs from being placed in disposals, as they were being
before.

code/modules/recycling/disposal-unit.dm

@@ -306,7 +306,7 @@
 		update()
 		return
 
-	if(!user.drop_item())
+	if(!user.drop_item() || I.flags & ABSTRACT) // Dunno why this wasn't here before?
 		return
 
 	I.loc = src