Require ScriptInstance to be valid in the editor debugger

This fixes an issue with visual scripts spamming error messages
in the editor when running the project with the remote scene tree
visible.

(cherry picked from commit 829c8247559a21d0b6f540e4a548d935c3a24643)

editor/script_editor_debugger.cpp

@@ -595,25 +595,25 @@ void ScriptEditorDebugger::_parse_message(const String &p_msg, const Array &p_da
 		le_clear->set_disabled(false);
 		le_set->set_disabled(false);
 	} else if (p_msg == "message:inspect_object") {
-		ScriptEditorDebuggerInspectedObject *debugObj = nullptr;
+		ScriptEditorDebuggerInspectedObject *debug_obj = nullptr;
 
 		ObjectID id = p_data[0];
 		String type = p_data[1];
 		Array properties = p_data[2];
 
 		if (remote_objects.has(id)) {
-			debugObj = remote_objects[id];
+			debug_obj = remote_objects[id];
 		} else {
-			debugObj = memnew(ScriptEditorDebuggerInspectedObject);
-			debugObj->remote_object_id = id;
-			debugObj->type_name = type;
-			remote_objects[id] = debugObj;
-			debugObj->connect("value_edited", this, "_scene_tree_property_value_edited");
+			debug_obj = memnew(ScriptEditorDebuggerInspectedObject);
+			debug_obj->remote_object_id = id;
+			debug_obj->type_name = type;
+			remote_objects[id] = debug_obj;
+			debug_obj->connect("value_edited", this, "_scene_tree_property_value_edited");
 		}
 
-		int old_prop_size = debugObj->prop_list.size();
+		int old_prop_size = debug_obj->prop_list.size();
 
-		debugObj->prop_list.clear();
+		debug_obj->prop_list.clear();
 		int new_props_added = 0;
 		Set<String> changed;
 		for (int i = 0; i < properties.size(); i++) {
@@ -646,12 +646,14 @@ void ScriptEditorDebugger::_parse_message(const String &p_msg, const Array &p_da
 					var = ResourceLoader::load(path);
 
 					if (pinfo.hint_string == "Script") {
-						if (debugObj->get_script() != var) {
-							debugObj->set_script(RefPtr());
+						if (debug_obj->get_script() != var) {
+							debug_obj->set_script(RefPtr());
 							Ref<Script> script(var);
 							if (!script.is_null()) {
-								ScriptInstance *script_instance = script->placeholder_instance_create(debugObj);
-								debugObj->set_script_and_instance(var, script_instance);
+								ScriptInstance *script_instance = script->placeholder_instance_create(debug_obj);
+								if (script_instance) {
+									debug_obj->set_script_and_instance(var, script_instance);
+								}
 							}
 						}
 					}
@@ -666,31 +668,31 @@ void ScriptEditorDebugger::_parse_message(const String &p_msg, const Array &p_da
 			}
 
 			//always add the property, since props may have been added or removed
-			debugObj->prop_list.push_back(pinfo);
+			debug_obj->prop_list.push_back(pinfo);
 
-			if (!debugObj->prop_values.has(pinfo.name)) {
+			if (!debug_obj->prop_values.has(pinfo.name)) {
 				new_props_added++;
-				debugObj->prop_values[pinfo.name] = var;
+				debug_obj->prop_values[pinfo.name] = var;
 			} else {
 				// Compare using `deep_equal` so dictionaries/arrays will be compared by value.
-				if (!debugObj->prop_values[pinfo.name].deep_equal(var)) {
-					debugObj->prop_values[pinfo.name] = var;
+				if (!debug_obj->prop_values[pinfo.name].deep_equal(var)) {
+					debug_obj->prop_values[pinfo.name] = var;
 					changed.insert(pinfo.name);
 				}
 			}
 		}
 
-		if (editor->get_editor_history()->get_current() != debugObj->get_instance_id()) {
-			editor->push_item(debugObj, "");
+		if (editor->get_editor_history()->get_current() != debug_obj->get_instance_id()) {
+			editor->push_item(debug_obj, "");
 		} else {
-			if (old_prop_size == debugObj->prop_list.size() && new_props_added == 0) {
+			if (old_prop_size == debug_obj->prop_list.size() && new_props_added == 0) {
 				//only some may have changed, if so, then update those, if exist
 				for (Set<String>::Element *E = changed.front(); E; E = E->next()) {
 					EditorNode::get_singleton()->get_inspector()->update_property(E->get());
 				}
 			} else {
 				//full update, because props were added or removed
-				debugObj->update();
+				debug_obj->update();
 			}
 		}
 	} else if (p_msg == "message:video_mem") {