FFmpeg: Make EncoderThread end-of-stream flag atomic


The flag is set from the source thread but read without the loop data
mutex by RecordingEngine::isEndOfSourceStreams(), a data race.

Pick-to: 6.12
Change-Id: Ib8dbc33247b4f29e8babdce7a66e8fcfdc4f09b4
Reviewed-by: Nils Petter Skålerud <nils.petter.skalerud@qt.io>
commit0a9305875688d55a38acde90728b7e3c9eb26a7e
parent48d162d1159f04963033fc51ebd43fdd9017623f
authorMikko Hallamaa <mikko.hallamaa@qt.io>
committerMikko Hallamaa <mikko.hallamaa@qt.io>
commit timeWed, 14 Oct 2026 11:08:27 +0000