ucm: arguments can't be numbers

[stew]

iif you run the getArgs builtin all of the numeric args are filtered. so in ucm, run:

> run getArgs one 2 three 4 five 6

and you only get the odd numbers:

["one", "three", "five"]

[ceedubs]

I think that this is the same as #2805 but how it manifests when there are no numbered args saved in the ucm session.

[aryairani]

#2805 did print the 1 though; are they getting filtered out or are they going in as normal strings? Here they're clearly being filtered out. The fix is the same though.

[sellout]

Yeah, this is a duplicate of #2805. At some point between then and now, un-assigned numbers started getting filtered.

There is probably a better option (e.g., warn or error on un-assigned numbers), but I think the filtering at least makes more sense than changing the behavior based on whether there are numbered args in the history is just likely to confuse users.