Fix memory corruption caused by rapid project/scene change

toonz/sources/toonzlib/tscenehandle.cpp

@@ -1,4 +1,4 @@
-
+#include <QTimer>
 
 #include "toonz/tscenehandle.h"
 
@@ -24,7 +24,22 @@ ToonzScene *TSceneHandle::getScene() const { return m_scene; }
 void TSceneHandle::setScene(ToonzScene *scene) {
   if (m_scene == scene) return;
   emit sceneSwitching();
-  delete m_scene;
+  ToonzScene *oldscene = m_scene;
   m_scene = scene;
   if (m_scene) emit sceneSwitched();
+
+  // Prevent memory corruption caused by delayed signals writing into the
+  // discarded old scene while that memory was freed.
+  // That made OT had a chance of crashing when project or scene changed rapidly.
+  // Note: This is not the best solution but "it just works"
+  if (oldscene) {
+    QTimer *delayedTimer = new QTimer(this);
+    delayedTimer->setSingleShot(true);
+
+    connect(delayedTimer, &QTimer::timeout, [=]() {
+      delete oldscene;
+      delayedTimer->deleteLater();
+    });
+    delayedTimer->start(3000);  // 1 sec was enough, but... dunno about toasters
+  }
 }