ResourceBrowser: stop preview when drag operation starts

Make sure preview is stopped as soon as a drag operation starts. This
is done by overloading QAbstractItemView::startDrag() and emit a signal
from there which is connected to an according slot in ResourceBrowser.

Signed-off-by: Tobias Doerffel <tobias.doerffel@gmail.com>

src/gui/ResourceTreeView.cpp

@@ -72,4 +72,13 @@ void ResourceTreeView::updateFilter( void )
 
 
 
+void ResourceTreeView::startDrag( Qt::DropActions supportedActions )
+{
+	emit dragStarted();
+
+	QTreeView::startDrag( supportedActions );
+}
+
+
+
 #include "moc_ResourceTreeView.cxx"