Check for multiplicative overflow in the wmem_alloc_array macros.

Bug:10343
Change-Id: Iea511c806b92999b3b497f94886c46a818100a23
Reviewed-on: https://code.wireshark.org/review/3396
Reviewed-by: Bill Meier <wmeier@newsguy.com>
(cherry picked from commit efb8a1ee4319593dc14b8a42068f2cfddea1bff5)
Reviewed-on: https://code.wireshark.org/review/3397
Reviewed-by: Evan Huus <eapache@gmail.com>