Make error handling safe in case pos is missing

mods/ENTITIES/mcl_mobs/api.lua

@@ -510,10 +510,12 @@ function mob_class:on_step(dtime)
 		else
 			warn_user_error ()
 			local pos = self.object:get_pos()
+			if pos then
 				local node = minetest.get_node(pos)
 				if node and node.name == "ignore" then
 					minetest.log("warning", "Pos is ignored: " .. dump(pos))
 				end
+			end
 			log_error (dump(retVal), dump(pos), dump(self))
 		end
 	else