gui: ipcworker,ipcserver: Refactor

Crashes were observed, faulting in libQtNetwork.
Those were rather rare. We also have no traces.

Probably depends on some order signal/slots were
processed. Remove shared states between connections,
such as the IPCPreviewWorker and socket instance in IPCServer.

gui/ipcpreviewworker.cpp

@@ -1,16 +1,50 @@
 #include <QtConcurrent>
 #include "ipcpreviewworker.h"
 #include "previewgeneratormapfunctor.h"
-IPCPreviewWorker::IPCPreviewWorker()
+IPCPreviewWorker::IPCPreviewWorker(QLocalSocket *peer)
 {
+	this->peer = peer;
 	this->connect(&previewWorkerWatcher, &QFutureWatcher<QByteArray>::resultReadyAt, this,
-				  [this](int index) { emit previewGenerated(previewWorkerWatcher.resultAt(index)); });
-	connect(&previewWorkerWatcher, &QFutureWatcher<QByteArray>::finished, this, [this] { emit finished(); });
+				  [this](int index)
+				  {
+					  if(this->peer != nullptr)
+					  {
+						  QDataStream stream{this->peer};
+						  stream << previewWorkerWatcher.resultAt(index);
+						  this->peer->flush();
+					  }
+				  });
+	connect(&previewWorkerWatcher, &QFutureWatcher<QByteArray>::finished, this, &IPCPreviewWorker::shutdownSocket);
+	connect(this->peer, &QLocalSocket::disconnected, this, &IPCPreviewWorker::shutdownSocket);
 }
 
-void IPCPreviewWorker::start(RenderConfig config, const QVector<RenderTarget> &targets, QLocalSocket *peer)
+void IPCPreviewWorker::shutdownSocket()
+{
+	if(cleaned)
+	{
+		return;
+	}
+	cleaned = true;
+	if(this->peer != nullptr)
+	{
+		if(this->peer->state() == QLocalSocket::ConnectedState)
+		{
+			this->peer->flush();
+			this->peer->waitForBytesWritten();
+			this->peer->disconnectFromServer();
+			if(this->peer->state() != QLocalSocket::UnconnectedState)
+			{
+				this->peer->waitForDisconnected();
+			}
+		}
+		delete this->peer;
+		this->peer = nullptr;
+	}
+	emit finished();
+}
+
+void IPCPreviewWorker::start(RenderConfig config, const QVector<RenderTarget> &targets)
 {
-	stop();
 	auto mapFunctor = PreviewGeneratorMapFunctor();
 	mapFunctor.setRenderConfig(config);