Remove column name validation from virtual layers queries

The query already went through the Sqlite query parser. So why not
trusting it? This was in the way of group by queries with count(*)
in the output fields.

src/providers/virtual/qgsvirtuallayerqueryparser.cpp

@@ -93,14 +93,6 @@ namespace QgsVirtualLayerQueryParser
     return defs;
   }
 
-  bool isValidColumnName( const QString& columnName )
-  {
-    // identifier name with possible accents
-    static QRegExp columnNameRx( "[a-zA-Z_\x80-\xFF][a-zA-Z0-9_\x80-\xFF]*" );
-
-    return columnNameRx.exactMatch( columnName );
-  }
-
 // set the type of the column type, given its text representation
   void setColumnDefType( const QString& columnType, ColumnDef& d )
   {
@@ -172,17 +164,6 @@ namespace QgsVirtualLayerQueryParser
       {
         QString columnName = q.columnText( 1 );
 
-        if ( !isValidColumnName( columnName ) )
-        {
-          qWarning() << "Invalid name: " << columnName;
-          hasInvalidName = true;
-
-          // add an unnamed column
-          ColumnDef d;
-          tableDef << d;
-          break;
-        }
-
         columns << columnName;
 
         QString columnType = q.columnText( 2 );

tests/src/python/test_provider_virtual.py

@@ -508,10 +508,11 @@ def test_sql3(self):
         QgsMapLayerRegistry.instance().addMapLayer(l2)
 
         # unnamed column
-        query = QUrl.toPercentEncoding("SELECT 42")
+        query = QUrl.toPercentEncoding("SELECT count(*)")
         l4 = QgsVectorLayer("?query=%s" % query, "tt", "virtual", False)
-        self.assertEqual(l4.isValid(), False)
-        self.assertEqual("Result column #1 has no name" in l4.dataProvider().error().message(), True)
+        self.assertEqual(l4.isValid(), True)
+        self.assertEqual(l4.dataProvider().fields().at(0).name(), "count(*)")
+        self.assertEqual(l4.dataProvider().fields().at(0).type(), QVariant.Int)
 
     def test_sql_field_types(self):
         query = QUrl.toPercentEncoding("SELECT 42 as t, 'ok'||'ok' as t2, GeomFromText('') as t3, 3.14*2 as t4")