giop: ignore NULL-terminator in CDR strings

CDR strings appear to be both counted *and* NULL-terminated in many cases,
which is rather weird, so if we see a NULL-terminator, ignore it in the count;
otherwise we print a trailing '\000' on all the strings we put in the tree.

Bug: 11126
Change-Id: I45b6b414683a6f646d37c2e2001b7319d5c80be5
Reviewed-on: https://code.wireshark.org/review/8390
Reviewed-by: Anders Broman <a.broman58@gmail.com>

epan/dissectors/packet-giop.c

@@ -3342,6 +3342,9 @@ guint32 get_CDR_string(tvbuff_t *tvb, const gchar **seq, int *offset, gboolean s
   }
   else if (slength > 0) {
     get_CDR_octet_seq(tvb, seq, offset, slength);
+    if (*seq[slength-1] == '\0') {
+      slength--;
+    }
   } else {
     *seq = wmem_strdup(wmem_packet_scope(), "");        /* zero-length string */
   }