gui: fix passing args to pdfviewer (paths with spaces work now)

gui/mainwindow.cpp

@@ -129,13 +129,14 @@ void MainWindow::pdfPreviewReceived(PdfPreview preview)
 					QString command = settings.value("pdfviewer").toString();
 					if(command != "" && command.contains("%p") && command.contains("%f"))
 					{
-						command = command.replace("%f", preview.documentPath);
-						command = command.replace("%p", QString::number(preview.page));
 						QStringList splitted = command.split(" ");
 						if(splitted.size() > 1)
 						{
 							QString cmd = splitted[0];
 							QStringList args = splitted.mid(1);
+							args.replaceInStrings("%f", preview.documentPath);
+							args.replaceInStrings("%p", QString::number(preview.page));
+
 							QProcess::startDetached(cmd, args);
 						}
 					}