Bug #437 - adds required validator to slug field for media edit'

otherwise we get a 404 because we navigate to blank slug

mediagoblin/edit/forms.py

@@ -23,7 +23,8 @@ class EditForm(wtforms.Form):
         'Title',
         [wtforms.validators.Length(min=0, max=500)])
     slug = wtforms.TextField(
-        'Slug')
+        'Slug',
+        [wtforms.validators.Required(message="The slug can't be empty")])
     description = wtforms.TextAreaField('Description of this work')
 
 class EditProfileForm(wtforms.Form):