Adds a small fix on walking interruption to avoid freed reference

addons/escoria-core/game/core-scripts/esc/commands/walk_block.gd

@@ -71,5 +71,6 @@ func run(command_params: Array) -> int:
 
 # Function called when the command is interrupted.
 func interrupt():
-	if walking_object_node != null and not walking_object_node is ESCPlayer:
+	if walking_object_node != null and is_instance_valid(walking_object_node) \
+			and not walking_object_node is ESCPlayer:
 		walking_object_node.stop_walking_now()