BMediaFile: fix MediaExtractor crash.

* stop the extractor processing before deleting the source.
* crash happened in MediaPlayer FilePlaylistItem::_CalculateDuration().
* was a regression introduced in hrev50671.
* fixes #13156.

headers/private/media/MediaExtractor.h

@@ -72,6 +72,9 @@ public:
 			status_t			GetStreamMetaData(int32 stream,
 									BMessage* _data) const;
 
+			void				StopProcessing();
+
+
 private:
 			void				_Init(BDataIO* source, int32 flags);
 

src/kits/media/MediaExtractor.cpp

@@ -147,13 +147,8 @@ MediaExtractor::~MediaExtractor()
 {
 	CALLED();
 
-#if !DISABLE_CHUNK_CACHE
-	// terminate extractor thread
-	delete_sem(fExtractorWaitSem);
-
-	status_t status;
-	wait_for_thread(fExtractorThread, &status);
-#endif
+	// stop the extractor thread, if still running
+	StopProcessing();
 
 	// free all stream cookies
 	// and chunk caches
@@ -412,6 +407,22 @@ MediaExtractor::GetStreamMetaData(int32 stream, BMessage* _data) const
 }
 
 
+void
+MediaExtractor::StopProcessing()
+{
+#if !DISABLE_CHUNK_CACHE
+	if (fExtractorWaitSem > -1) {
+		// terminate extractor thread
+		delete_sem(fExtractorWaitSem);
+		fExtractorWaitSem = -1;
+
+		status_t status;
+		wait_for_thread(fExtractorThread, &status);
+	}
+#endif
+}
+
+
 void
 MediaExtractor::_RecycleLastChunk(stream_info& info)
 {

src/kits/media/MediaFile.cpp

@@ -471,6 +471,12 @@ BMediaFile::_UnInit()
 	free(fTrackList);
 	fTrackList = NULL;
 	fTrackNum = 0;
+
+	// Tells the extractor to stop its asynchronous processing
+	// before deleting its source
+	if (fExtractor != NULL)
+		fExtractor->StopProcessing();
+
 	if (fDeleteSource) {
 		delete fSource;
 		fSource = NULL;