wally_psbt_output_taproot_keypath_add() is not idempotent #509
Description
I tried to sign an already-signed PSBT in core lightning, and we aborted because wally_psbt_output_taproot_keypath_add() failed.
wally_map_keypath_add() works fine (handing take_value=true, ignore_dups=true) to add_map(). But then wally_map_merkle_path_add() fails, as that sets take_value=false, ignore_dups=false.
As a workaround I'm just failing in this case, but it seems like it would be nice if it worked, as it did pre-taproot?