Fix language-environment and font selection on MS-Windows

Fix language-environment and font selection on MS-Windows

These changes improve setting the language-environment and font
selection when MS-Windows returns useless "ZZZ" as the "language
name", which then disrupts all the setup of the locale-dependent
stuff, and in particular font selection.
* lisp/w32-fns.el (w32-charset-info-alist): Add an element for
"iso8859-5", in case LANG is set to something unusable, like
"ZZZ".  This allows fonts capable of displaying Cyrillic
characters to be used even when language preferences are screwed.

* src/w32.c (init_environment): If GetLocaleInfo returns "ZZZ" as
the "language name" for LOCALE_USER_DEFAULT, try again with locale
ID based on what GetUserDefaultUILanguage returns.  (Bug#39286)