agent: Fix two compiler warnings.
* agent/command.c (cmd_preset_passphrase, pinentry_loopback): Use %zu in format string. * scd/ccid-driver.c (ccid_get_atr): Ditto. * agent/command-ssh.c (stream_read_string): Init arg STRING_SIZE to avoid maybe_unitialized warning.
Actually the first one might have been a problem on big endian
machines.
- Signed-off-by: Werner Koch <wk@gnupg.org>