Fix checking of vasprintf() return value
Fix checking of vasprintf() return value

The (res == NULL) check below should not be necessary per (info libc),
but doesn't hurt, so I have left it in.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

deirf/libumberlog