libbinder_ndk: more accurate error for array allocator failure

The allocator can fail due to no memory.
In the non-nullable case, it can also fail if the array is null. So we
return STATUS_UNEXPECTED_NULL in those cases.

Test: run the following with local changes to remove the oemlock HIDL
service and applying patchset 2 of ag/20460045
Test: atest GtsOemLockServiceTestCases
Bug: na

Change-Id: I385780cd407e2d0b5707032ff39ae20c937eea66