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.

core/object.cpp

@@ -1366,7 +1366,10 @@ 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/editor_inspector.cpp

@@ -470,10 +470,12 @@ bool EditorPropertyRevert::can_property_revert(Object *p_object, const StringNam
 
 	if (!has_revert && !p_object->get_script().is_null()) {
 		Ref<Script> scr = p_object->get_script();
-		Variant orig_value;
-		if (scr->get_property_default_value(p_property, orig_value)) {
-			if (orig_value != p_object->get(p_property)) {
-				has_revert = true;
+		if (scr.is_valid()) {
+			Variant orig_value;
+			if (scr->get_property_default_value(p_property, orig_value)) {
+				if (orig_value != p_object->get(p_property)) {
+					has_revert = true;
+				}
 			}
 		}
 	}
@@ -668,11 +670,13 @@ void EditorProperty::_gui_input(const Ref<InputEvent> &p_event) {
 
 			if (!object->get_script().is_null()) {
 				Ref<Script> scr = object->get_script();
-				Variant orig_value;
-				if (scr->get_property_default_value(property, orig_value)) {
-					emit_changed(property, orig_value);
-					update_property();
-					return;
+				if (scr.is_valid()) {
+					Variant orig_value;
+					if (scr->get_property_default_value(property, orig_value)) {
+						emit_changed(property, orig_value);
+						update_property();
+						return;
+					}
 				}
 			}
 

scene/main/node.cpp

@@ -2421,7 +2421,7 @@ 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);