skip multi-column field instead of just warning

Simply warning doesn't actually fix any problem, but replaces the earlier TypeError with another TypeError. So, continue in case of a multi-column field to skip it.

flask_admin/contrib/sqla/view.py

@@ -393,6 +393,7 @@ class ModelView(BaseModelView):
 
                     if len(filtered) > 1:
                         warnings.warn('Can not convert multiple-column properties (%s.%s)' % (self.model, p.key))
+                        continue
 
                     column = filtered[0]
                 else: