lib: Use /dev/zero instead of /dev/stderr in test-istream-unix unit test Some distros don't seem to allow opening stderr.
lib: Use /dev/zero instead of /dev/stderr in test-istream-unix unit test
Some distros don't seem to allow opening stderr.

dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot