Terminate IPTV read thread on demux close

IPTV reading thread doesn't have a termination condition. This CL
adds a flag mIsIptvReadThreadTerminated which tracks whether the
thread resources should be cleaned up.

Bug: 288170590
Test: atest VtsHalTvTunerTargetTest
Change-Id: I3a19e1045ee67dac2d95457d217adb1375674ed4