Merge pull request #1368 from PlasmaPower/user-exists-value-error

Catch a ValueError when checking if a user exists

src/borg/testsuite/platform.py

@@ -40,7 +40,7 @@ def user_exists(username):
     try:
         pwd.getpwnam(username)
         return True
-    except KeyError:
+    except (KeyError, ValueError):
         return False