[fix] Crash on non-existing variable

If personal access token can't be queried due to some DB issue, then
it crashes on reading an unset variable.

Author: bruntib

web/server/codechecker_server/session_manager.py

@@ -623,6 +623,7 @@ def __try_personal_access_token(self, auth_string):
             return None
 
         user_name, token = auth_string.split(':', 1)
+        personal_access_token = None
 
         transaction = None
         try: