token-cli: don't error when missing default config

[2501babe]

fixes a regression introduced in #3166. prior to that, the config argument would default to the value of solana_cli_config::CONFIG_FILE, and loading the config would fall back to a default if it failed. changing the to an error protected against a missing file provided by --config, but also errored in the default case if they lacked the default file

this change distinguishes the three cases, erroring if the user provided a bad --config option, but falling back to defaults if they didnt

[joncinque]

Nice catch, thanks

Pull request has been modified.

[joncinque]

of course it fails right before your new test... you can rebase on top of #3425, if you want to take your chances

[joncinque]

#3425 landed, so if you don't mind rebasing once more, we can be sure that this is good to go

[2501babe]

taking the cowards way out and deleting the test i attempted to add, it turns out spl-token address (and, in fact, every non-help command) attempts to load the signer keypair from its expected path and fails if its not there, and i cant tell it to use a different path in a test with a non-default config because thats... what the config does. and i dont want to write a key out to the default location and pollute a shared resource, if later tests end up depending on something else being there

there should be more comprehensive integration tests for the binary (pre this patch it crashed unconditionally on my machine) but thats a different thing imo

[joncinque]

I think #3293 will at least address the config issue. Definitely happy to come up with a better testing strategy!