Minor cleanup

flask_admin/form/upload.py

@@ -85,11 +85,7 @@ class ImageUploadInput(object):
         }
 
         if field.data and isinstance(field.data, string_types):
-            if field.thumbnail_size:
-                url = url_for(field.endpoint, filename=field.thumbnail_fn(field.data))
-            else:
-                url = url_for(field.endpoint, filename=field.data)
-
+            url = self.get_url()
             args['image'] = html_params(src=url)
 
             template = self.data_template
@@ -98,6 +94,12 @@ class ImageUploadInput(object):
 
         return HTMLString(template % args)
 
+    def get_url(self, field):
+        if field.thumbnail_size:
+            return url_for(field.endpoint, filename=field.thumbnail_fn(field.data))
+
+        return url_for(field.endpoint, filename=field.data)
+
 
 # Fields
 class FileUploadField(fields.TextField):