[SERVER][BUGFIX] Layer order from group

If custom order is not enabled and a group is requested, layers was added in
 the DOM element order. The default endering order is the reverse.

To fix this issue, QgsWMSProjectParser::addLayersFromGroup has to read group
 element children from end (bottom) to start (top).

src/server/qgswmsprojectparser.cpp

@@ -258,7 +258,8 @@ void QgsWMSProjectParser::addLayersFromGroup( const QDomElement& legendGroupElem
   {
     QMap< int, QDomElement > layerOrderList;
     QDomNodeList groupElemChildren = legendGroupElem.childNodes();
-    for ( int i = 0; i < groupElemChildren.size(); ++i )
+    // for rendering layers has to be add from bottom (end) to top (start)
+    for ( int i = groupElemChildren.size()-1; i >= 0 ; --i )
     {
       QDomElement elem = groupElemChildren.at( i ).toElement();
       if ( elem.tagName() == "legendgroup" )