TunerHAL Fix filterDispatcher returning false

The Dvr::startFilterDispatcher method is intended to
call the startFilterHandler method on every filter by using
pass through methods in the Demux. However, the method
currently returns early with a failure (false return value)
whenever isVirtualFrontend and isRecording are both false.
This causes the thread that the method is called from to
immediately log and exit.

This error occurs when the Dvr::startFilterDispatcher
method is called from the Dvr threadloop, but not when it
is called from the Demux threadloop due to their different
parameters. As noted by current bug 239731089, this means
that this error is only exhibited inconsistently due to
a race condition.

Bug: 237718541
Test: Manually using Cuttlefish, as well as VTS. Previous
inconsistent Dvr filtering errors no longer occur.

Change-Id: I677b66bdc0dacf1a7d57bcbd3085ffd6475547dd