Object::script may not be a valid Ref<Script>

It appears that Object::script may be a valid ScriptInstance but not be
castable to Ref<Script>. There were only 5 places in the code that made
this assumption. This commit fixes that.

(cherry picked from commit 20b0046945)

core/object.cpp

@@ -1330,7 +1330,10 @@ Array Object::_get_incoming_connections() const {
 void Object::get_signal_list(List<MethodInfo> *p_signals) const {
 
 	if (!script.is_null()) {
-		Ref<Script>(script)->get_script_signal_list(p_signals);
+		Ref<Script> scr = script;
+		if (scr.is_valid()) {
+			scr->get_script_signal_list(p_signals);
+		}
 	}
 
 	ClassDB::get_signal_list(get_class_name(), p_signals);

editor/property_editor.cpp

@@ -2397,6 +2397,7 @@ void PropertyEditor::_check_reload_status(const String &p_name, TreeItem *item)
 
 	if (!has_reload && !obj->get_script().is_null()) {
 		Ref<Script> scr = obj->get_script();
+		if (scr.is_valid()) {
 			Variant orig_value;
 			if (scr->get_property_default_value(p_name, orig_value)) {
 				if (orig_value != obj->get(p_name)) {
@@ -2404,6 +2405,7 @@ void PropertyEditor::_check_reload_status(const String &p_name, TreeItem *item)
 				}
 			}
 		}
+	}
 
 	if (found != -1 && !has_reload) {
 
@@ -3558,6 +3560,7 @@ void PropertyEditor::update_tree() {
 
 		if (!has_reload && !obj->get_script().is_null()) {
 			Ref<Script> scr = obj->get_script();
+			if (scr.is_valid()) {
 				Variant orig_value;
 				if (scr->get_property_default_value(p.name, orig_value)) {
 					if (orig_value != obj->get(p.name)) {
@@ -3566,6 +3569,7 @@ void PropertyEditor::update_tree() {
 					}
 				}
 			}
+		}
 
 		if (_might_be_in_instance() && !has_reload && item->get_cell_mode(1) == TreeItem::CELL_MODE_RANGE && item->get_text(1) == String()) {
 			item->add_button(1, get_icon("ReloadEmpty", "EditorIcons"), 3, true);
@@ -3950,11 +3954,13 @@ void PropertyEditor::_edit_button(Object *p_item, int p_column, int p_button) {
 
 		if (!obj->get_script().is_null()) {
 			Ref<Script> scr = obj->get_script();
+			if (scr.is_valid()) {
 				Variant orig_value;
 				if (scr->get_property_default_value(prop, orig_value)) {
 					_edit_set(prop, orig_value);
 				}
 			}
+		}
 
 	} else {
 

scene/main/node.cpp

@@ -2560,7 +2560,7 @@ void Node::_replace_connections_target(Node *p_new_target) {
 
 		if (c.flags & CONNECT_PERSIST) {
 			c.source->disconnect(c.signal, this, c.method);
-			bool valid = p_new_target->has_method(c.method) || p_new_target->get_script().is_null() || Ref<Script>(p_new_target->get_script())->has_method(c.method);
+			bool valid = p_new_target->has_method(c.method) || Ref<Script>(p_new_target->get_script()).is_null() || Ref<Script>(p_new_target->get_script())->has_method(c.method);
 			ERR_EXPLAIN("Attempt to connect signal \'" + c.source->get_class() + "." + c.signal + "\' to nonexistent method \'" + c.target->get_class() + "." + c.method + "\'");
 			ERR_CONTINUE(!valid);
 			c.source->connect(c.signal, p_new_target, c.method, c.binds, c.flags);