Allow filters in WFST for multiple geometry columns. r=bartvde (closes #3370)

lib/OpenLayers/Format/WFST/v1.js

@@ -432,8 +432,8 @@ OpenLayers.Format.WFST.v1 = OpenLayers.Class(OpenLayers.Format.XML, {
                 this.setFilterProperty(filter.filters[i]);
             }
         } else {
-            if(filter instanceof OpenLayers.Filter.Spatial) {
-                // got a spatial filter, set its property
+            if(filter instanceof OpenLayers.Filter.Spatial && !filter.property) {
+                // got a spatial filter without property, so set it
                 filter.property = this.geometryName;
             }
         }