agetty: return proper value if compiled without ISSUEDIR support

agetty: return proper value if compiled without ISSUEDIR support

If agetty is compiled without support for ISSUEDIR, then it implements
a stub for `issuedir_read` that simply does nothing. In fact it does
too little, as it doesn't have a proper return statement even though the
function returns an integer.

Fix the issue by always returning `1` from `issuedir_read`. This
is the same error code that the real implementation of that function
returns in case it cannot open the directory and is thus a sensible
default to pretend that the directory doesn't exist.

Signed-off-by: Patrick Steinhardt <ps@pks.im>