Invalid value for field alarm when using khal new -i leads to crash

Describe the bug
Invalid value for field alarm when using khal new -i leads to crash.

If applicable: Stack Trace

Traceback (most recent call last):
  File "/nix/store/2ksnys3k9gfvfd864d2cqybzm18qbwa2-khal-0.11.3/bin/.khal-wrapped", line 9, in <module>
    sys.exit(main_khal())
             ^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/9l7cdymnw9ck7l7hk1d7n6yc2ql3a0j0-python3.12-click-8.1.7/lib/python3.12/site-packages/click/decorators.py", line 33, in new_func
    return f(get_current_context(), *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/2ksnys3k9gfvfd864d2cqybzm18qbwa2-khal-0.11.3/lib/python3.12/site-packages/khal/cli.py", line 393, in new
    new_func(
  File "/nix/store/2ksnys3k9gfvfd864d2cqybzm18qbwa2-khal-0.11.3/lib/python3.12/site-packages/khal/controllers.py", line 378, in new_interactive
    edit_event(event, collection, conf['locale'], width=term_width)
  File "/nix/store/2ksnys3k9gfvfd864d2cqybzm18qbwa2-khal-0.11.3/lib/python3.12/site-packages/khal/controllers.py", line 535, in edit_event
    alarm_trig = -1 * parse_datetime.guesstimedeltafstr(a.strip())
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/2ksnys3k9gfvfd864d2cqybzm18qbwa2-khal-0.11.3/lib/python3.12/site-packages/khal/parse_datetime.py", line 296, in guesstimedeltafstr
    raise ValueError(f'Invalid beginning of timedelta string "{delta_string}": "{tups[0]}"')
ValueError: Invalid beginning of timedelta string "alarm": "alarm"

To Reproduce

khal new -i
summary: test3
datetime range: now tomorrow
timezone [Europe/Berlin]: 
description (or 'None'): None
event saved
Edit?  do[n]e  [s]ummary  [d]escription  da[t]etime range  re[p]eat  [l]ocation  [c]ategories  [a]larm  [D]elete  [u]rl: a
alarm (or "None") [None]: alarm

OS, version, khal version and how you installed it:

• khal, version 0.11.3
• Python 3.12.7
• OS: NixOS
• installed via nixpkgs (nix-shell -p khal)

Start in khal/controllers.py at edit_event and follow its call to parse_datetime.py:guesstimedeltafstr. Reproduce the issue with khal new -i and an invalid alarm value; done means that input is handled without an unhandled traceback, with the expected behavior established from the surrounding code.