Fix infinite loop for when port max range is -1

Fix infinite loop for when port max range is -1

Due to integer overflow (unsigned -1 + 1 = 0), a call to
dissector_add_uint_range would be stuck in an infinite loop, eventually
crashing due to out of memory.

Found when setting radius.alternate_port:-1, but could happen with any
dissector using similar ports_range constructs.

Change-Id: Ia234e94516446250e959e0f51d552bef704cddff
Reviewed-on: https://code.wireshark.org/review/13153
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>