amqp: Fix a number of bugs in dissect_amqp_0_10_map().

 (Among other things: "2 ^ xxx" is *not* 2 to the xxx'th power).

Change-Id: I893b72e853ecbb5d7e6259e950fb347e89eed6c2
Reviewed-on: https://code.wireshark.org/review/5109
Reviewed-by: Bill Meier <wmeier@newsguy.com>