packet-amqp.c: 2nd try: Temporary/preliminary fix for Bug #10582 (crash)

  This is a temporary/preliminary fix to prevent the buildbot fuzz-test
   failures seen when testing the capture file attached to Bug #10582.

  This "2nd try" is an attempt to prevent the Wireshark 1.12 fuzzbot
  from failing.

  As noted in the bug, a complete fix will require some reworking of
    the amqp dissector.

Change-Id: I497b661b3b72704a74022ea6081b7fa09fcccc14
Reviewed-on: https://code.wireshark.org/review/4967
Reviewed-by: Bill Meier <wmeier@newsguy.com>