Return better error code for some getinfo IPC commands.

* agent/command.c (cmd_getinfo): Return GPG_ERR_FALSE as boolean False.
* g13/server.c (cmd_getinfo): Ditto.
* sm/server.c (cmd_getinfo): Ditto.

GPG_ERR_FALSE was introduced with libgpg-error 1.21 and we now require
a later version for gnupg 2. Thus we can switch to this more
descriptive code.

• Signed-off-by: Werner Koch <wk@gnupg.org>