Check the final reallocation for adding the terminating NULL and handle
it just like those in the loop. Simply use REFTABLE_ALLOC_GROW instead
of keeping the REFTABLE_REALLOC_ARRAY call and adding code to preserve
the original pointer value around it.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>