boon-reset-state-for-switchw: Accept a frame as the argument

[ttuegel]

window-selection-change-functions may be called with a frame instead of a window when the selected frame has changed. In particular, this happens at startup when the initial frame is created. When compiled natively, the type mismatch (framep instead of windowp) may cause a segmentation fault.

[ttuegel]

This still isn't enough: I get segfaults with native compilation on some machines (but not others), so I'm going back to the drawing board.