Bug 1788182

Description of problem:
I was testing a repo I created using `dnf reposync` but used the wrong syntax for `--repofrompath`: I put the URL first instead of the repo name. My mistake, but it caused an unhandled exception.

Version-Release number of selected component:
dnf-4.2.17-1.fc31

Additional info:
reporter:       libreport-2.11.3
cmdline:        /usr/bin/python3 /usr/bin/dnf --repofrompath /mnt/nas/repo/mirror2/centos/8/2020-01-06/extras,extras --repo extras list
crash_function: __init__
exception_type: RuntimeError
executable:     /usr/bin/dnf
interpreter:    python3-3.7.5-2.fc31.x86_64
kernel:         5.3.15-300.fc31.x86_64
runlevel:       N 5
type:           Python3
uid:            1000

Truncated backtrace:
repo.py:440:__init__:RuntimeError: Bad id for repo: /mnt/nas/repo/mirror2/centos/8/2020-01-06/extras, byte = / 0

Traceback (most recent call last):
  File "/usr/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.7/site-packages/dnf/cli/main.py", line 191, in user_main
    errcode = main(args)
  File "/usr/lib/python3.7/site-packages/dnf/cli/main.py", line 65, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.7/site-packages/dnf/cli/main.py", line 94, in _main
    cli.configure(list(map(ucd, args)), option_parser())
  File "/usr/lib/python3.7/site-packages/dnf/cli/cli.py", line 969, in configure
    self._configure_repos(opts)
  File "/usr/lib/python3.7/site-packages/dnf/cli/cli.py", line 753, in _configure_repos
    this_repo = self.base.repos.add_new_repo(label, self.base.conf, baseurl=[path])
  File "/usr/lib/python3.7/site-packages/dnf/repodict.py", line 86, in add_new_repo
    repo = dnf.repo.Repo(repoid, conf)
  File "/usr/lib/python3.7/site-packages/dnf/repo.py", line 427, in __init__
    self._repo = libdnf.repo.Repo(name if name else "", self._config)
  File "/usr/lib64/python3.7/site-packages/libdnf/repo.py", line 440, in __init__
    _repo.Repo_swiginit(self, _repo.new_Repo(id, config))
RuntimeError: Bad id for repo: /mnt/nas/repo/mirror2/centos/8/2020-01-06/extras, byte = / 0

Local variables in innermost frame:
self: <libdnf.repo.Repo;  >
id: '/mnt/nas/repo/mirror2/centos/8/2020-01-06/extras'
config: <libdnf.conf.ConfigRepo; proxy of <Swig Object of type 'libdnf::ConfigRepo *' at 0x7f2e3cc733c0> >