Fix unit tests with new license support

Make the license field in the forms optional and let them
properly be defaulted to "".

mediagoblin/edit/forms.py

@@ -42,6 +42,7 @@ class EditForm(wtforms.Form):
             "You usually don't need to change this."))
     license = wtforms.SelectField(
         _('License'),
+        [wtforms.validators.Optional(),],
         choices=licenses_as_choices())
 
 class EditProfileForm(wtforms.Form):

mediagoblin/edit/views.py

@@ -75,9 +75,7 @@ def edit_media(request, media):
             media.description_html = cleaned_markdown_conversion(
                 media.description)
 
-            media.license = (
-                unicode(request.POST.get('license'))
-                or '')
+            media.license = unicode(request.POST.get('license', ''))
 
             media.slug = unicode(request.POST['slug'])