mediacodec: fix use-after-free

changed milestone to %4.0

added Component::Decoders Hw Platform::Android labels

It looks OK, but I don't understand the "can be used from the video context". If that means it can be used from a picture context release, it might need to be refcounted with the pictures it relates to.

The whole sys is refcounted, but this particular object was deleted from pf_destroy nonetheless.

Nice catch!

I don't remember exactly why the two are not completely tied. IIRC flush or something else would lead to the destruction of the data in queued pictures, especially in transcode scenario, so the decoder instance is actually tied to the video context instead of the destruction of the decoder_t.

Nevertheless, I also find the commit message confusing. Maybe something in the lines of what follow would improve it?

mediacodec: release timestamp_fifo with video context

`CleanInputVideo()` is linked to the input side of the decoder (.pf_decode) but
`video.timestamp_fifo` can be used from the output side (threads from mediacodec)
and is actually also tied to the lifecycle of the video context, as visible in the
destructor `CloseDecoder`. Since the lifecycle of the video context is at least
the one from the input side, destroy the timestamp_fifo there.

Fixes a use-after-free when the video context is not released from CloseDestructor()
while mediacodec is still running (not joined yet).

Regression from cdff503e

Also, if I follow correctly, cdff503e established the baseline for the code but 57323dda is the commit that deferred the destruction and allowed this case to happen.