Don't require history to calculate anon disk usage

This is probably the simplest way to fix the anon user issue.
If we don't have a history the size is 0, that's fairly simple.

We might still want to do galaxyproject#17755
for those FastAPI endpoints that do actually require a default history.

lib/galaxy/webapps/galaxy/services/users.py

@@ -122,10 +122,9 @@ def get_user(self, trans: ProvidesUserContext, user_id):
     def _anon_user_api_value(self, trans: ProvidesHistoryContext):
         """Return data for an anonymous user, truncated to only usage and quota_percent"""
         if not trans.user and not trans.history:
-            # Can't return info about this user, may not have a history yet.
-            # return {}
-            raise glx_exceptions.MessageException(err_msg="The user has no history, which should always be the case.")
-        usage = self.quota_agent.get_usage(trans, history=trans.history)
+            usage = None
+        else:
+            usage = self.quota_agent.get_usage(trans, history=trans.history)
         percent = self.quota_agent.get_percent(trans=trans, usage=usage)
         usage = usage or 0
         return {