Tuner HAL Fix bug allowing only one MediaEvent

Currently, our startMediaFilterHandler returns on the first
time it successfully creates a MediaEvent. This does not
match the intended behavior, which is that all of its
current output is read and turned into events, and then
cleared.

Bug: 238797398
Test: Manually with Cuttlefish and SampleTunerTvInput.
Before change, any input type except ES will only create a
single MediaEvent. After change, full input will be handled
properly.

Change-Id: I856385cdf8ebb3a7d3fb0f864085123ec6c172b9