This bug was found by the mrt regress test. The problem is that
an empty ASPATH has lenght 0 and ibuf_open(0) fails (currently this is the
case but I had this changed in my work tree so I did not notice that).

Use a simple hack to allocate an extra byte so ibuf_open() succeeds.
With this the mrt regress is happy again. If we change the ibuf_open()
behaviour this can be reverted.

-- 
:wq Claudio

Index: util.c
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/util.c,v
diff -u -p -r1.80 util.c
--- util.c	30 Jan 2024 13:50:09 -0000	1.80
+++ util.c	2 Feb 2024 11:38:27 -0000
@@ -547,8 +547,12 @@ aspath_inflate(struct ibuf *in)
 	uint16_t	 short_as;
 	uint8_t		 seg_type, seg_len;
 
-	/* allocate enough space for the worst case */
-	if ((out = ibuf_open(ibuf_size(in) * 2)) == NULL)
+	/*
+	 * allocate enough space for the worst case,
+	 * add 1 byte for the empty ASPATH case since we can't
+	 * allocate an ibuf of 0 length.
+	 */
+	if ((out = ibuf_open(ibuf_size(in) * 2 + 1)) == NULL)
 		return (NULL);
 
 	/* then copy the aspath */