Doors: Same prediction change for trapdoors

Forgot this in the last commit, thanks @Fixer-007

mods/doors/init.lua

@@ -608,6 +608,7 @@ function doors.register_trapdoor(name, def)
 
 			return secret, "a locked trapdoor", owner
 		end
+		def.node_dig_prediction = ""
 	else
 		def.on_blast = function(pos, intensity)
 			minetest.remove_node(pos)