window cleanup at exit

window cleanup at exit

exit_nhwindows() is called before terminate(), and the tty incarnation
destroys all windows--including 'pickinv_cache_win'--without setting
the various index variables used to access them to WIN_ERR, then
terminate() calls freedynamicdata() which calls free_pickinv_cache()
which tries to destroy 'pickinv_cache_win' since it isn't WIN_ERR (if
the perm_invent option has been enabled during that playing session).
Some of the other <interface>_exit_nhwindows() also tear things down
without resetting the variables used to track them, so fixing this in
exit_nhwindows() would have been pretty messy.

Call free_pickinv_cache() before exit_nhwindows() in done().  At the
moment it's only called from done(), so other exit paths won't release
the small chunk(s) of memory used for the alternate inventory window
(if it got created for perm_invent support).