fix: make util.get_model_fields() work with more model classes

should not restrict to classes inheriting from wuttjamaican base, any
sqlalchemy class should work

src/wuttaweb/util.py

@@ -462,14 +462,13 @@ def get_model_fields(config, model_class=None):
     if not model_class:
         return
 
-    app = config.get_app()
-    model = app.model
-    if not issubclass(model_class, model.Base):
-        return
-
-    mapper = sa.inspect(model_class)
-    fields = [prop.key for prop in mapper.iterate_properties]
-    return fields
+    try:
+        mapper = sa.inspect(model_class)
+    except sa.exc.NoInspectionAvailable:
+        pass
+    else:
+        fields = [prop.key for prop in mapper.iterate_properties]
+        return fields
 
 
 def make_json_safe(value, key=None, warn=True):