(reorder_font_vector): Pay attention to the case that

(reorder_font_vector): Pay attention to the case that
the 3rd element of font_def is nil.
(fontset_font): For the default fontset, append one more fontset
elements for a script-based font specification.  Don't add script
attribute on finding a font.
(new_fontset_from_font): Unconditionally set FONTSET_ASCII to the
font name.
(fontset_ascii_font): If a font can't be opened, return nil.