owner_api_listen_port missing field in grin-wallet.toml

[antiochp]

Related #2475.

A new config item was added in #2475 -

owner_api_listen_port

We need to be able to safely handle the case where this is missing (i.e. all existing wallets).

Otherwise the wallet fails to startup successfully with a missing field error.

[antiochp]

Not sure if the solution here is to recreate the config file (and fill in any missing values), or to safely handle this value as optional.

@yeastplume What's the recommended fix here? I know you've worked on some reading/rewriting config files stuff.

[antiochp]

Note: workaround is to add it manually to grin-wallet.toml -

owner_api_listen_port = 3420

[yeastplume]

for backwards compat it needs to be an Option in the internal struct, then have something set it to the default value if it’s missing when read