[JSON] Allow UTF-8 characters in parsed strings (rdkcentral#1532)

Co-authored-by: Pierre Wielders <[email protected]>

Source/core/JSON.h

@@ -1947,7 +1947,7 @@ namespace Core {
                         } else if (current == '\"') {
                             // We are done! leave this element.
                             finished = true;
-                        } else if (current <= 0x1F) {
+                        } else if (static_cast<std::make_unsigned<TCHAR>::type>(current) <= 0x1F) {
                             error = Error{ "Unescaped control character detected" };
                         } else {
                             // Just copy and onto the next;