don't access empty range list, could be rhbz#1180312

ScRangeList::DeleteArea() may remove an entire range, if it was the
last range a subsequent call to ScConditionalFormat::DeleteArea() would
attempt to access an invalid first element.

Change-Id: I8d68c27963dc8561d61a94980093c271bd3aaffb

sc/source/core/data/conditio.cxx

@@ -2063,6 +2063,9 @@ void ScConditionalFormat::UpdateMoveTab( sc::RefUpdateMoveTabContext& rCxt )
 
 void ScConditionalFormat::DeleteArea( SCCOL nCol1, SCROW nRow1, SCCOL nCol2, SCROW nRow2 )
 {
+    if (maRanges.empty())
+        return;
+
     SCTAB nTab = maRanges[0]->aStart.Tab();
     maRanges.DeleteArea( nCol1, nRow1, nTab, nCol2, nRow2, nTab );
 }