plugin-cln-xpay: Not redirecting with unknown arguments

[bittylicious]

The latest LNBits seems to send pay requests with description arguments.

As I have the xpay-handle-pay true configuration value set, this results in the error plugin-cln-xpay: Not redirecting pay (unknown arg "description") error, and frankly falling back to the non-xpay functionality rarely works for me.

Can we somehow make this switch simply try its best, rather than dying when an unknown argument pops up? I understand that LNBits doesn't want to support custom payment commands for each back end.