amqp: Fix for crash reported in Bug 10582.

  Detect and handle overflows when advancing 'offset'.

  (This patch converts the previous temporary fix to be the
   permanent fix for Wireshark-1.10).

Ping Bug 10582
Change-Id: I6ed10c325d851ad9fa5e13e1852fe86ad6f09f6d
Reviewed-on: https://code.wireshark.org/review/5196
Reviewed-by: Bill Meier <wmeier@newsguy.com>