VstPlugin: flush temporary data exchange file

VstPlugin creates a temporary file for exchanging data chunks of VST
plugins with the remote process. After calling QFile::write(...) data
has not neccessarily been written due to QFile's internal write buffer.
Therefore explicitely call QFile::flush() so all data is guaranteed
to be written.

Fixes problems with plugins which save small data chunks.
(cherry picked from commit 4b8ddcc14f)

plugins/vst_base/VstPlugin.cpp

@@ -419,6 +419,8 @@ void VstPlugin::loadChunk( const QByteArray & _chunk )
 	if( tf.open() )
 	{
 		tf.write( _chunk );
+		tf.flush();
+
 		lock();
 		sendMessage( message( IdLoadSettingsFromFile ).
 				addString(