WebmFrameThread: Don't set mDone in WebmFrameSinkThread::stop

WebmFrameSinkThread::stop shouldn't set mDone to true, it will
be set once EOS frames are handled in WebmFrameSinkThread::run

Bug: 177376580
Bug: 267933226
Test: atest CtsMediaV2TestCases:EncoderProfileLevelTest
Test: atest CtsMediaV2TestCases:MuxerTest
Test: atest CtsMediaV2TestCases:MuxerUnitTest

Change-Id: I0e3bd689b4284104ed8d9e7a84f78598ca413615
diff --git a/media/libstagefright/webm/WebmFrameThread.cpp b/media/libstagefright/webm/WebmFrameThread.cpp
index 59ce8db..cdbd745 100644
--- a/media/libstagefright/webm/WebmFrameThread.cpp
+++ b/media/libstagefright/webm/WebmFrameThread.cpp
@@ -197,7 +197,6 @@
 }
 
 status_t WebmFrameSinkThread::stop() {
-    mDone = true;
     mVideoFrames.push(WebmFrame::EOS);
     mAudioFrames.push(WebmFrame::EOS);
     return WebmFrameThread::stop();