FIX(client): Improve handling of the GlobalShortcutButtons dialog

This commit makes the shortcut configuration dialog a modal window.
It also explicitly searches for a parent QDialog, such that the window
can be centered over the Mumble application instead of randomly out of bounds
of the screen. (This is most likely only necessary because of a bug in Qt, but
Qt is a pain to debug)

Fixes mumble-voip#5024

src/mumble/GlobalShortcutButtons.cpp

@@ -8,15 +8,41 @@
 
 #include "GlobalShortcut.h"
 
+#include "MainWindow.h"
 #include "Global.h"
 
+#include <QDebug>
+#include <QRect>
 #include <QTimer>
 
 GlobalShortcutButtons::GlobalShortcutButtons(QWidget *parent) : QDialog(parent), m_ui(new Ui::GlobalShortcutButtons) {
 	m_ui->setupUi(this);
+	setModal(true);
 
 	connect(m_ui->addButton, &QPushButton::toggled, this, &GlobalShortcutButtons::toggleCapture);
 	connect(m_ui->removeButton, &QPushButton::clicked, this, &GlobalShortcutButtons::removeItem);
+
+	// Due to what appears to be a Qt bug, this dialog will not take
+	// the parent geometry into account when spawning.
+	// Therefore, we search for a different parent or even fallback to the
+	// MainWindow and move this dialog to its center.
+	QWidget *searchWidget = parent;
+	while (searchWidget && !qobject_cast< QDialog * >(searchWidget)) {
+		searchWidget = searchWidget->parentWidget();
+	}
+	QWidget *effectiveParent = qobject_cast< QDialog * >(searchWidget);
+	if (Global::get().mw && Global::get().mw->isVisible()) { //! effectiveParent &&
+		effectiveParent = Global::get().mw;
+	}
+
+	QTimer::singleShot(0, [effectiveParent, this]() {
+		if (!effectiveParent) {
+			return;
+		}
+		QRect geometry = effectiveParent->geometry();
+		qDebug() << geometry;
+		move(geometry.center().x() - (width() / 2), geometry.center().y() - (height() / 2));
+	});
 }
 
 GlobalShortcutButtons::~GlobalShortcutButtons() {