Fix for CONPY-213

Additionally to the fix for CONPY-214 (which fixed the iterator), we
need to check that converter will not be called with EOF (None).

mariadb/cursors.py

@@ -353,7 +353,7 @@ def _fetch_row(self):
         if not self.field_count:
              raise mariadb.ProgrammingError("Cursor doesn't have a result set")
         row= super().fetchone()
-        if self._connection._converter:
+        if self._connection._converter and row:
             l= list(row)
             if not self._description:
                 self._description= super().description

testing/test/integration/test_cursor.py

@@ -1333,7 +1333,18 @@ def test_conpy209(self):
         self.assertEqual(transformed, cursor._transformed_statement)
         del cursor
 
-
+    def test_conpy213(self):
+        conversions= { **{FIELD_TYPE.NEWDECIMAL : float}}
+        connection = create_connection({"converter": conversions})
+        cursor= connection.cursor()
+        cursor.execute("SELECT 1.1")
+        rows= cursor.fetchall()
+        self.assertEqual(rows[0][0], 1.1)
+        cursor.execute("SELECT 1.1")
+        row= cursor.fetchone()
+        self.assertEqual(row[0], 1.1)
+        del cursor
+        del connection
 
     def test_conpy91(self):
         with create_connection() as connection: