1.7.3 gui editor crash in GuiTreeViewCtrl

I 'think' I was resizing the extents of a control when this occurred. Since I was running debug (no engine folder changes), I hit debug on the crash. I'm not sure the cause of this, but it was a "indexing outside of vector bounds" assertion on this line in GuiTreeViewCtrl::onMouseDragged.

if (mPreviousDragCell >= 0)
      mVisibleItems[mPreviousDragCell]->mState.clear( Item::MouseOverBmp | Item::MouseOverText );

mPreviousDragCell was 7 at the time, and mVisibleItems' element count was 4.