itemmodels.AbstractSortTableModel: Fix mapFromSourceRows

Author: janezd

Orange/widgets/utils/itemmodels.py

@@ -127,7 +127,10 @@ def mapToSourceRows(self, rows):
             Source rows matching input rows. If they are the same,
             simply input `rows` is returned.
         """
-        if self.__sortInd is not None:
+        if self.__sortInd is not None \
+                # self.__sortInd[rows] fails if `rows` is an empty list or array
+                and (isinstance(rows, (int, type(Ellipsis)))
+                     or len(rows)):
             new_rows = self.__sortInd[rows]
             if rows is Ellipsis:
                 new_rows.setflags(write=False)