Comment 2 for bug 661777

Here's a quick emergency patch to prevent the crash. The crash happens because in WTrackTableView::dropEvent() selectedRows, which is a QList, gets empty when auto crossfade starts. Calling first() or last() on an empty QList causes this assert.

The attached patch is for 1.8 branch. It may not a perfect fix (I couldn't really test it, because auto dj in 1.8 didn't work for me), but at least Mixxx won't crash. The crash is also reproducible with trunk r2621.