journald: fix vacuuming of archived journals

d_name is modified on line 227 so if the entire journal name is needed
again p must be used. Before this change when journal_file_empty was called
on archived journals it would always return with -2.

Signed-off-by: George McCollister <george.mccollister@gmail.com>
journald: fix fd leak in journal_file_empty

Before my previous patch, journal_file_empty wasn't be called with the
correct filename. Now that it's being called with the correct filename
it leaks file descriptors. This patch closes the file descriptors before
returning.

Signed-off-by: George McCollister <george.mccollister@gmail.com>

[Edit harald@redhat.com: make use of _cleanup_close_ instead]