RFC on SDL_SetWindowPosition change to support moving window between monitors

This bug contains a patch that allows one to specify the SDL_WINDOWPOS_CENTERED(disply#) to the SDL_SetWindowPosition and have that function respect the display number to easily allow moving a window between monitors.

https://bugzilla.libsdl.org/show_bug.cgi?id=2849

I would like some comments on the patch I provided for this as well as the change that it makes.

Edward Rudd
OutOfOrder.cc
Skype: outoforder_cc
317-366-7906