Error e-mails contain UID if known

Closes #99.

owl/error_mail.py

@@ -3,7 +3,7 @@
 import datetime
 import email.message
 import email.headerregistry
-from flask import Flask, request
+from flask import Flask, request, g
 import subprocess
 import token_bucket
 import traceback
@@ -25,6 +25,8 @@ def log_flask_exception(app: Flask, exc_info) -> None:
         'Referrer': request.referrer,
         'Client': request.remote_addr,
     }
+    if hasattr(g, 'uid'):
+        attrs['UID'] = g.uid
     log_exception(app, request.path, attrs, exc_info)