WaE: comparison of constant 255 with expression of type 'const char'

Better fix for warning: "comparison of constant 255 with expression of
type 'const char' is always true". I hadn't considered that the code
is in a template, so it must handle strings of arbitrary integer types
(well, Unicode).

Change-Id: I38d6d480bfc3ff89db1276cac38d310ecdcc2cfa

external/boost/boost.jsonparser.warnings.patch.0

@@ -63,7 +63,7 @@
              // handle high unicode characters.
              if (*b == 0x20 || *b == 0x21 || (*b >= 0x23 && *b <= 0x2E) ||
 -                (*b >= 0x30 && *b <= 0x5B) || (*b >= 0x5D && *b <= 0xFF))
-+                (*b >= 0x30 && *b <= 0x5B) || (*b >= 0x5D))
++                (*b >= 0x30 && *b <= 0x5B) || (*b >= 0x5D && static_cast<typename std::basic_string<Ch>::traits_type::int_type>(*b) <= 0xFF))
                  result += *b;
              else if (*b == Ch('\b')) result += Ch('\\'), result += Ch('b');
              else if (*b == Ch('\f')) result += Ch('\\'), result += Ch('f');