LP360: avoid double-removal of floating dock containers (#838)

In DockManagerPrivate::restoreStateFromXml() the floating widgets were
removed via removeDockContainer() and then queued for deletion with
deleteLater(). When ~CDockContainerWidget() ran it would call
removeDockContainer() a second time on the same container, tripping the
Q_ASSERT(removed == 1) check in CDockManager::removeDockContainer().

Switch to CDockContainerWidget::removeFromDockManager() (introduced in
upstream 544c624) so the container's back-pointer to the manager is
cleared up front and the destructor becomes a no-op for the manager
side. This keeps the LP360_AI workspace restore path crash-free until
the equivalent fix lands upstream.

Author: fdarmayan

src/DockManager.cpp

@@ -349,7 +349,12 @@ bool DockManagerPrivate::restoreStateFromXml(const QByteArray &state,  int versi
 		{
 			CFloatingDockContainer* floatingWidget = FloatingWidgets[i];
 			if (!floatingWidget) continue;
-			_this->removeDockContainer(floatingWidget->dockContainer());
+			// Use removeFromDockManager() (introduced in upstream commit 544c624) instead
+			// of removeDockContainer() so the container's back-pointer to the manager is
+			// cleared. Otherwise ~CDockContainerWidget() (called when deleteLater() fires)
+			// would try to remove this container a second time, tripping the
+			// Q_ASSERT(removed == 1) check in CDockManager::removeDockContainer().
+			floatingWidget->dockContainer()->removeFromDockManager();
 			floatingWidget->deleteLater();
 		}
     }