winrt: Assert and warnings when closing application.

Failed to completely destroy window resources, likely because the application is shutting down (The operation cannot be completed because the window is being closed.)

QCoreApplication::exit: It is not recommended to explicitly exit an application on Windows Store Apps

ASSERT failure in __cdecl QWinRTWindow::QWinRTWindow(class QWindow *): "The operation cannot be completed because the window is being closed.", file qt5\qtbase\src\plugins\platforms\winrt\qwinrtwindow.cpp, line 147

ASSERT failure in void __cdecl QWinRTWindow::setGeometry(const class QRect &): "The operation cannot be completed because the window is being closed.", file qt5\qtbase\src\plugins\platforms\winrt\qwinrtwindow.cpp, line 239

Failed to completely destroy window resources, likely because the application is shutting down (The operation cannot be completed because the window is being closed.)

ASSERT failure in __cdecl QWinRTIntegration::~QWinRTIntegration(void): "A method was called at an unexpected time.", file qt5\qtbase\src\plugins\platforms\winrt\qwinrtintegration.cpp, line 157

Failed to unregister screen event callbacks (The operation cannot be completed because the window is being closed.)

First-chance exception at 0x77CB35D7 (KERNELBASE.DLL) in The callee (server [not server application]) is not available and disappeared; all connections are invalid. The call did not execute.