Fixes an (unreported?) issue with invalid MSSQL data items

The issue was triggered when refreshing the browser with an
invalid MSSQL connection, the Populated state was never set
and the spinning icon was shown forever.

src/providers/mssql/qgsmssqldataitems.cpp

@@ -136,6 +136,7 @@ QVector<QgsDataItem *> QgsMssqlConnectionItem::createChildren()
   if ( !QgsMssqlConnection::openDatabase( db ) )
   {
     children.append( new QgsErrorItem( this, db.lastError().text(), mPath + "/error" ) );
+    setAsPopulated();
     return children;
   }