more robust way of getting WFS geometry

wfs/__init__.py

@@ -144,11 +144,12 @@ class WFS(OWS):
         """
 
         geomType = layer.GetGeomType()
-        if geomType == 0:
+        if geomType == 0: # unknown
             # brutal force way
             f = layer.GetNextFeature()
-            gr = f.GetGeometryRef()
-            geomType = gr.GetGeometryType()
+            if f:
+                gr = f.GetGeometryRef()
+                geomType = gr.GetGeometryType()
 
         if geomType in [ogr.wkbPolygon,
                         ogr.wkbMultiPolygon,