After explorer is restarted while show-in-taskbar is false, toggling
show-in-taskbar no longer puts mpv back to the taskbar until it's
unfocused and refocused.
My guess of how this works is that the HWND of the taskbar is cached,
and setting the WS_EX_TOOLWINDOW style internally uses this value to
show/hide the taskbar button. But after explorer is restarted it no
longer works until its taskbar state needs to change (such as focusing).
Only then it realizes the HWND is no longer valid and refreshes it.
Fix this by following MS documentation on this: the window needs to be
hidden before changing the style, and be shown after that. This
unfortunately can sometimes introduce a brief window flash, but it
fixes the problem.
93708a9d38