jp2uc/up2jc: avoid crash due to invalid pointer

Commit 4356ccd ("towupper/towlower: handle Turkic language special
casing") changed the locale pointer in calls to towctrans_l from a NULL
pointer to LC_GLOBAL_LOCALE, which is defined as -1.

Unfortunately jp2uc_l/up2jc_l just expect a NULL or non-NULL pointer,
so LC_GLOBAL_LOCALE as input is derefenced later on and the call crashes.

To fix this problem, handle LC_GLOBAL_LOCALE just as if a NULL pointer
has been passed to the function.  Keep the NULL pointer handling intact
for backward compatibility.

Fixes: 4356ccd ("towupper/towlower: handle Turkic language special casing")
Reported-by: Christophe Lyon <christophe.lyon.oss@gmail.com>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Author: github-cygwin

newlib/libc/ctype/jp2uc.c

@@ -166,7 +166,8 @@ __uc2jp (wint_t c, int type)
 wint_t
 _jp2uc_l (wint_t c, struct __locale_t * l)
 {
-  const char * cs = l ? __locale_charset(l) : __current_locale_charset();
+  const char *cs = (l && l != LC_GLOBAL_LOCALE)
+		   ? __locale_charset(l) : __current_locale_charset();
   if (0 == strcmp (cs, "JIS"))
     c = __jp2uc (c, JP_JIS);
   else if (0 == strcmp (cs, "SJIS"))
@@ -179,14 +180,15 @@ _jp2uc_l (wint_t c, struct __locale_t * l)
 wint_t
 _jp2uc (wint_t c)
 {
-  return _jp2uc_l (c, 0);
+  return _jp2uc_l (c, NULL);
 }
 
 /* Unicode to Japanese conversion interface */
 wint_t
 _uc2jp_l (wint_t c, struct __locale_t * l)
 {
-  const char * cs = l ? __locale_charset(l) : __current_locale_charset();
+  const char *cs = (l && l != LC_GLOBAL_LOCALE)
+		   ? __locale_charset(l) : __current_locale_charset();
   if (0 == strcmp (cs, "JIS"))
     c = __uc2jp (c, JP_JIS);
   else if (0 == strcmp (cs, "SJIS"))