HDMI-CEC: Adding null exception catch related to mHdmiConnection

In a scenario where HdmiCecController calls nativeGetHpdSignalType,
and mHdmiConnection is a null object triggering a NullPointerException,
which leads to a system_server crash, therefore adding a catch for
NullPointerException.

Bug: b/376776151
Flag: EXEMPT bug fix only
Test: Success to catch NullPointerObject exception.

Change-Id: I286cbbb3de9c5127b1bc9ffee376a9be2e4f764a