lib: replace Json::Reader by CharReader

In commit gromox-3.1-45-ga15d0275d, rfbl.cpp was switched away from
streambuf, but in doing so, started using a deprecated jsoncpp API
accidentally. There was a __attribute__((deprecated)) warning, but
only until jsoncpp 1.9.5^2~1.

Author: jengelh

lib/rfbl.cpp

@@ -1468,7 +1468,9 @@ errno_t gx_compress_tofile(std::string_view inbuf, const char *outfile,
 
 bool str_to_json(std::string_view sv, Json::Value &jv)
 {
-	return Json::Reader().parse(sv.data(), sv.data() + sv.size(), jv);
+	using reader_t = decltype(Json::CharReaderBuilder().newCharReader());
+	std::unique_ptr<std::remove_pointer_t<reader_t>> rd(Json::CharReaderBuilder().newCharReader());
+	return rd->parse(sv.data(), sv.data() + sv.size(), &jv, nullptr);
 }
 
 std::string json_to_str(const Json::Value &jv)