MediaSourcePrivateRemote incorrectly uses its own m_sourceBuffers array, it should be using the one from the base class. it was missed in 270354@main
<rdar://problem/119694935>
Pull request: https://github.com/WebKit/WebKit/pull/21839
Committed 272098@main (ab512fb562c3): <https://commits.webkit.org/272098@main> Reviewed commits have been landed. Closing PR #21839 and removing active labels.