UI: Fix closing OBS before showing whats new dialog

The program can get stuck waiting for the browser within a event queue,
so instead mark that the program is closing, do it in a separate thread,
signal the window when it's finished, and then check whether it's in the
process of closing before actually showing the dialog.

UI/win-update/win-update.cpp

@@ -20,8 +20,15 @@
 #include <winhttp.h>
 #include <shellapi.h>
 
+#ifdef BROWSER_AVAILABLE
+#include <browser-panel.hpp>
+#endif
+
 using namespace std;
 
+struct QCef;
+extern QCef *cef;
+
 /* ------------------------------------------------------------------------ */
 
 #ifndef WIN_MANIFEST_URL
@@ -799,3 +806,13 @@ try {
 } catch (string &text) {
 	blog(LOG_WARNING, "%s: %s", __FUNCTION__, text.c_str());
 }
+
+/* ------------------------------------------------------------------------ */
+
+void WhatsNewBrowserInitThread::run()
+{
+#ifdef BROWSER_AVAILABLE
+	cef->wait_for_browser_init();
+#endif
+	emit Result(url);
+}

UI/win-update/win-update.hpp

@@ -33,3 +33,17 @@ signals:
 public:
 	inline WhatsNewInfoThread() {}
 };
+
+class WhatsNewBrowserInitThread : public QThread {
+	Q_OBJECT
+
+	QString url;
+
+	virtual void run() override;
+
+signals:
+	void Result(const QString &url);
+
+public:
+	inline WhatsNewBrowserInitThread(const QString &url_) : url(url_) {}
+};