Incorrect use of check_public_key() in `id` command

When working on #237 (closed), and looking where check_public_key() is used, I found a place where it is improperly used.

The boolean return value is used in id to check whether the parameter is well a pubkey. But, check_public_key() returns True in case of a valid pubkey (and a valid corresponding checksum if specified). But, returns False in two cases: wrong pubkey format, and wrong checksum. Thus, the id command thinks the False means the parameter is not a pubkey, but an uid.

In most cases this is fine, but if you specify a wrong checksum, then the id commands thinks this is an uid, and therefore try to find it on the network rather than stopping saying this is a wrong checksum.

This is not super critical, but this should be addressed one day.