Fix pinentry loopback and passphrase contraints.
* agent/command.c (cmd_get_passphrase): Don't repeat passphrase for pinentry loopback mode. * agent/genkey.c (check_passphrase_constraints): Immediately return when pinentry mode is loopback.
Fixes endless loop when inquiring a passphrase with
pinentry-mode=loopback that may not satisfy passphrase contraints.