Fix clip move incorrectly rejected

Fixes #869

src/timeline2/model/timelinemodel.cpp

@@ -2352,7 +2352,7 @@ bool TimelineModel::requestGroupMove(int itemId, int groupId, int delta_track, i
                 if (getTrackById_const(current_track_id)->hasStartMix(item.first)) {
                     subPlaylist = m_allClips[item.first]->getSubPlaylistIndex();
                 }
-                if (!getTrackById_const(current_track_id)->isAvailable(target_position, -delta_pos, subPlaylist)) {
+                if (!getTrackById_const(current_track_id)->isAvailable(target_position, playtime, subPlaylist)) {
                     if (!getTrackById_const(current_track_id)->isBlankAt(current_in - 1)) {
                         // No move possible, abort
                         bool undone = local_undo();