These would accidentally get a titlebar because the "borderless" style mask
is zero but the resizable attribute adds a bit. I assume this happens because
you used to need window decoration to resize a window in macOS, but this
changed in later releases.
This only caused problems when recreating a window (you had an
SDL_WINDOW_OPENGL window and tried to create a Metal SDL_Renderer on it, etc).
Fixes#4324.
8527c583f4