Description of problem:
Using "legendary" without login causes an exception, instead of a short error that tells me I didn't log in (and how to log in)

Version-Release number of selected component:
legendary-0.20.5-1.fc33

Additional info:
reporter:       libreport-2.14.0
cgroup:         0::/user.slice/user-1000.slice/user/app.slice/app-org.gnome.Terminal.slice/vte-spawn-c3e8d23b-28ff-422a-a0cc-260d3b4a3e6b.scope
cmdline:        /usr/bin/python3 /usr/bin/legendary install 'Jurassic World Evolution'
crash_function: login
exception_type: ValueError
executable:     /usr/bin/legendary
interpreter:    python3-3.9.1-1.fc33.x86_64
kernel:         5.9.15-200.fc33.x86_64
runlevel:       N 5
type:           Python3
uid:            1000

Truncated backtrace:
core.py:155:login:ValueError: No saved credentials

Traceback (most recent call last):
  File "/usr/bin/legendary", line 33, in <module>
    sys.exit(load_entry_point('legendary-gl==0.20.5', 'console_scripts', 'legendary')())
  File "/usr/lib/python3.9/site-packages/legendary/cli.py", line 1342, in main
    cli.install_game(args)
  File "/usr/lib/python3.9/site-packages/legendary/cli.py", line 529, in install_game
    if not self.core.login():
  File "/usr/lib/python3.9/site-packages/legendary/core.py", line 155, in login
    raise ValueError('No saved credentials')
ValueError: No saved credentials

Local variables in innermost frame:
self: <legendary.core.LegendaryCore object at 0x7ff1003f4730>