Make sure the previewWaitCondition.wakeAll() is heard by using the proper lock.

Author: daniel-kristjansson

mythtv/libs/libmythtv/previewgenerator.cpp

@@ -88,6 +88,7 @@ void PreviewGenerator::SetOutputFilename(const QString &fileName)
 
 void PreviewGenerator::TeardownAll(void)
 {
+    QMutexLocker locker(&previewLock);
     previewWaitCondition.wakeAll();
     listener = NULL;
 }