Resolves tdf#88485: Allow to select rightmost symbols in the dialog

by adjusting target area with proper offsets.

Change-Id: I66100c898354909623991c3af3e78287d6f5a9a0
Reviewed-on: https://gerrit.libreoffice.org/23147Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

starmath/source/dialog.cxx

@@ -1186,6 +1186,8 @@ void SmShowSymbolSetWindow::MouseButtonDown(const MouseEvent& rMEvt)
     GrabFocus();
 
     Size aOutputSize(nColumns * nLen, nRows * nLen);
+    aOutputSize.Width() += nXOffset;
+    aOutputSize.Height() += nYOffset;
     Point aPoint(rMEvt.GetPosPixel());
     aPoint.X() -= nXOffset;
     aPoint.Y() -= nYOffset;