msvcrt: Fix wctob in C locale.

dlls/msvcrt/tests/string.c

@@ -2002,6 +2002,9 @@ static void test_wctob(void)
     ret = p_wctob(0x81);
     ok(ret == (int)(char)0x81, "ret = %x\n", ret);
 
+    ret = p_wctob(0x9f);
+    ok(ret == (int)(char)0x9f, "ret = %x\n", ret);
+
     ret = p_wctob(0xe0);
     ok(ret == (int)(char)0xe0, "ret = %x\n", ret);
 }

dlls/msvcrt/wcs.c

@@ -1056,8 +1056,14 @@ INT CDECL MSVCRT_wctob( MSVCRT_wint_t wchar )
 {
     char out;
     BOOL error;
+    UINT codepage = get_locinfo()->lc_codepage;
 
-    if(WideCharToMultiByte( get_locinfo()->lc_codepage, 0, &wchar, 1, &out, 1, NULL, &error ) && !error)
+    if(!codepage) {
+        if (wchar < 0xff)
+            return (signed char)wchar;
+        else
+            return MSVCRT_EOF;
+    } else if(WideCharToMultiByte( codepage, 0, &wchar, 1, &out, 1, NULL, &error ) && !error)
         return (INT)out;
     return MSVCRT_EOF;
 }