Add bounds check to sensors direct channel creation

Avoids attempting to read a 0-size array during input validation. Adds
SafetyNet logging when this is triggered.

Also, change the cast for the ashmem size check from int to int64_t to
avoid potential conversion to negative number on 32-bit systems.

Bug: 70986337
Test: run POC, confirm via logs that function bails early
Change-Id: I674285738983f18de3466f9e818d83dabe269b7d