Fix speaker view for eventyay-video (#145)

* send invitation for additional speaker input
* issue with speaker view
* remove url import from other branch

src/pretalx/api/serializers/speaker.py

@@ -61,12 +61,12 @@ def get_avatar(obj):
 
     @staticmethod
     def get_avatar_source(obj):
-        if obj.user.has_avatar:
+        if obj.user.has_avatar and obj.user.avatar_source != '':
             return obj.user.avatar_source(event=obj.event)
 
     @staticmethod
     def get_avatar_license(obj):
-        if obj.user.has_avatar:
+        if obj.user.has_avatar and obj.user.avatar_license != '':
             return obj.user.avatar_license(event=obj.event)
 
     @staticmethod