RemotePlugin: always use installation directory as working directory

On Windows the working directory is not set to the installation directory
when launching LMMS by opening an associated project file. Because of this
the RemotePlugin programs can't be launched as the required DLL files are
missing.

Closes #351.

src/core/RemotePlugin.cpp

@@ -139,6 +139,7 @@ bool RemotePlugin::init( const QString &pluginExecutable,
 	args << QString::number( in()->shmKey() );
 #ifndef DEBUG_REMOTE_PLUGIN
 	m_process.setProcessChannelMode( QProcess::ForwardedChannels );
+	m_process.setWorkingDirectory( QCoreApplication::applicationDirPath() );
 	m_process.start( exec, args );
 	m_watcher.start( QThread::LowestPriority );
 #else