w32: Fix some warnings reported by -Wall -Wextra.

w32: Fix some warnings reported by -Wall -Wextra.

* lib-src/ntlib.c: Include <ctype.h>.

* nt/cmdproxy.c: Include <ctype.h>.
  (make_absolute): Remove unused variable `i'.

* src/w32fns.c (x_set_menu_bar_lines): Remove unused variable `olines'.
  (w32_wnd_proc): Pass NULL to Windows API, not uninitialized buffer.
  (Fx_close_connection): Remove unused variable `i'.

* src/w32font.c (w32font_draw): Return number of glyphs.
  (w32font_open_internal): Remove unused variable `i'.
  (w32font_driver): Add missing initializer.

* src/w32menu.c (utf8to16): Remove unused variable `utf16'.
  (fill_in_menu): Remove unused variable `items_added'.

* src/w32term.c (last_mouse_press_frame): Remove static global variable.
  (w32_clip_to_row): Remove unused variable `f'.
  (x_delete_terminal): Remove unused variable `i'.

* src/w32uniscribe.c (uniscribe_shape): Remove unused variable `nclusters'.
  (NOTHING): Remove unused static global variable.
  (uniscribe_check_otf): Remove unused variable `table'.
  (uniscribe_font_driver): Add missing initializers.