fix: startup, report nicer error in case DB is damaged or empty when starting services

rhodecode/config/utils.py

@@ -102,6 +102,9 b' def get_default_user_id():'
         result = session.execute(text(
             "SELECT user_id from users where username = :uname"
         ), {'uname': DEFAULT_USER})
-        user_id = result.first()[0]
+        user = result.first()
+        if not user:
+            raise ValueError('Unable to retrieve default user data from DB')
+        user_id = user[0]
 
     return user_id