Platform: fix a handle leak in Windows-specific DPI scaling code.

Rather unlikely to be hit in practice because the default is virtual DPI
scaling and this is just a fallback, but still.

src/Magnum/Platform/Sdl2Application.cpp

@@ -418,6 +418,9 @@ Vector2 Sdl2Application::dpiScalingInternal(const Implementation::Sdl2DpiScaling
     #elif defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
     HDC hDC = GetWindowDC(nullptr);
     Vector2i monitorSize{GetDeviceCaps(hDC, HORZSIZE), GetDeviceCaps(hDC, VERTSIZE)};
+    /* The handle is apparently allocated anew each time, so we have to release
+       it back: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getwindowdc#remarks */
+    ReleaseDC(nullptr, hDC);
     SDL_DisplayMode mode;
     CORRADE_INTERNAL_ASSERT(SDL_GetDesktopDisplayMode(0, &mode) == 0);
     auto dpi = Vector2{Vector2i{mode.w, mode.h}*25.4f/Vector2{monitorSize}};