getstate: fix access type and remove redundant cast

getstate: fix access type and remove redundant cast

WM_STATE is defined to be format == 32 which xlib returns as
`long` and so accessing it as `unsigned char` is incorrect.

and also &p is already an `unsigned char **` and so the cast was
completely redundant.

given the redundant cast, i assume `p` was `long *` at some time
but was changed to `unsigned char *` later, but the pointer
access (and the cast) wasn't updated.

also add a `format == 32` check as safety measure before
accessing, just in case.