reftable: handle realloc error in parse_names()

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>

reftable/basics.c

@@ -241,7 +241,8 @@ char **parse_names(char *buf, int size)
 		p = next + 1;
 	}
 
-	REFTABLE_REALLOC_ARRAY(names, names_len + 1);
+	if (REFTABLE_ALLOC_GROW(names, names_len + 1, names_cap))
+		goto err;
 	names[names_len] = NULL;
 
 	return names;