Fix bufferhubd crash in buffer_hub-test

Add some null and valid check in constructors to prevent bufferhubd from
crash when user enter invalid params.

Test: "atest frameworks/native/libs/vr/libbufferhub/buffer_hub-test.cpp#TestCreateBufferHubBufferFails"
and check "adb logcat | grep bufferhub"
No crashing reports.
atest buffer_hub-test: passed
Fix: 118624156

Change-Id: I56e83808f38ab146f1fc61d1b736dd0be640503d