url: do not continue HTTP authentication with user=None (issue6425)
I initially thought this is a py3-compat bug of passwordmgr._writedebug(),
but actually returning (None, str) pair is wrong at all. HTTP authentication
would continue with user="None" in that case.
Since registering a password of user=None should also be wrong, this patch
simply adds early return.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..