Table: Fix non-string metas filtering

OWSelectRows widget crashed, when filtering discrete meta attribute (if metas consist of both, discrete and string attributes).
Used condition was "is defined".

Author: VesnaT

Orange/data/table.py

@@ -1122,6 +1122,7 @@ def _filter_values_indicators(self, filter):
             if isinstance(f, data_filter.FilterDiscrete) and f.values is None \
                     or isinstance(f, data_filter.FilterContinuous) and \
                                     f.oper == f.IsDefined:
+                col = col.astype(float)
                 if conjunction:
                     sel *= ~np.isnan(col)
                 else:

Orange/tests/test_table.py

@@ -1022,6 +1022,12 @@ def test_valueFilter_string_is_defined(self):
         x = filter.Values([f])(d)
         self.assertEqual(len(x), 7)
 
+    def test_valueFilter_discrete_meta_is_defined(self):
+        d = data.Table("test9.tab")
+        f = filter.FilterDiscrete(-4, None)
+        x = filter.Values([f])(d)
+        self.assertEqual(len(x), 8)
+
     def test_valueFilter_string_case_sens(self):
         d = data.Table("zoo")
         col = d[:, "name"].metas[:, 0]