Fix regresion on Texture Region Editor Plugin. Fixes#9282

editor/plugins/texture_region_editor_plugin.cpp

@@ -218,7 +218,7 @@ void TextureRegionEditor::_region_input(const Ref<InputEvent> &p_input) {
 		mtx.xform(rect.position + Vector2(0, rect.size.y / 2)) + Vector2(-4, 0)
 	};
 
-	Ref<InputEventMouseButton> mb;
+	Ref<InputEventMouseButton> mb = p_input;
 	if (mb.is_valid()) {
 
 		if (mb->get_button_index() == BUTTON_LEFT) {