[BUGFIX] QGIS Server segfault when features does not have the same fields as the layer.

In some WFS GetFeature request, with Filter or FeatureId, all the fields are not well loaded in the feature.

To fix it, we just verifying that the attribute index is lesser than the feature fields count.

Fixes #14619

Author: rldhont

src/server/qgswfsserver.cpp

@@ -1897,6 +1897,10 @@ QString QgsWFSServer::createFeatureGeoJSON( QgsFeature* feat, int prec, QgsCoord
   for ( int i = 0; i < attrIndexes.count(); ++i )
   {
     int idx = attrIndexes[i];
+    if ( idx >= fields->count() )
+    {
+      continue;
+    }
     QString attributeName = fields->at( idx ).name();
     //skip attribute if it is excluded from WFS publication
     if ( excludedAttributes.contains( attributeName ) )
@@ -1992,6 +1996,10 @@ QDomElement QgsWFSServer::createFeatureGML2( QgsFeature* feat, QDomDocument& doc
   for ( int i = 0; i < attrIndexes.count(); ++i )
   {
     int idx = attrIndexes[i];
+    if ( idx >= fields->count() )
+    {
+      continue;
+    }
     QString attributeName = fields->at( idx ).name();
     //skip attribute if it is excluded from WFS publication
     if ( excludedAttributes.contains( attributeName ) )
@@ -2065,6 +2073,10 @@ QDomElement QgsWFSServer::createFeatureGML3( QgsFeature* feat, QDomDocument& doc
   for ( int i = 0; i < attrIndexes.count(); ++i )
   {
     int idx = attrIndexes[i];
+    if ( idx >= fields->count() )
+    {
+      continue;
+    }
     QString attributeName = fields->at( idx ).name();
     //skip attribute if it is excluded from WFS publication
     if ( excludedAttributes.contains( attributeName ) )