Better workaround for VMS getnameinfo() bug

The actual bug with current getnameinfo() on VMS is not that it puts
gibberish in the service buffer, but that it doesn't touch it at all.
The gibberish we dealt with before was simply stuff that happened to
be on the stack.

It's better to initialise the service buffer properly (with the empty
string) and check if it's still an empty string after the
getnameinfo() call, and fill it with the direct numerical translation
of the raw port if that's the case.
Reviewed-by: NRich Salz <rsalz@openssl.org>

crypto/bio/b_addr.c

@@ -229,7 +229,7 @@ static int addr_strings(const BIO_ADDR *ap, int numeric,
     if (1) {
 #ifdef AI_PASSIVE
         int ret = 0;
-        char host[NI_MAXHOST], serv[NI_MAXSERV];
+        char host[NI_MAXHOST] = "", serv[NI_MAXSERV] = "";
         int flags = 0;
 
         if (numeric)
@@ -252,11 +252,13 @@ static int addr_strings(const BIO_ADDR *ap, int numeric,
             return 0;
         }
 
-        /* VMS getnameinfo() seems to have a bug, where serv gets filled
-         * with gibberish.  We can at least check for digits when flags
-         * has NI_NUMERICSERV enabled
+        /* VMS getnameinfo() has a bug, it doesn't fill in serv, which
+         * leaves it with whatever garbage that happens to be there.
+         * However, we initialise serv with the empty string (serv[0]
+         * is therefore NUL), so it gets real easy to detect when things
+         * didn't go the way one might expect.
          */
-        if ((flags & NI_NUMERICSERV) != 0 && !isdigit(serv[0])) {
+        if (serv[0] == '\0') {
             BIO_snprintf(serv, sizeof(serv), "%d",
                          ntohs(BIO_ADDR_rawport(ap)));
         }