ThermalManagerService: initialize to THROTTLING_NONE explicitly

When there is no HAL connection or HAL malfunctioning, thermal status
will stay in an invalid value, which would be returned when client
register status callback.

This CL will opportunistically assume system is in "NONE" throttling
when in above states such as no HAL connection or HAL malfunctioning.

Bug: 155772239
Test: atest ThermalManagerServiceTest
Test: atest PowerManagerTest
Test: atest thermalmanager-test
Change-Id: I9fceb5ef6f8b9a23983b7b93200f381eaf23a77b