Use unsigned type in percent_encoding to prevent overflow for %80..%ff

Related fix in Boost.Spirit 80414bc688

CHANGELOG.md

@@ -2,6 +2,7 @@
   - Changes from 5.14.3:
     - Bugfixes:
       - FIXED #4704: Fixed regression in bearings reordering introduced in 5.13 [#4704](https://github.com/Project-OSRM/osrm-backend/issues/4704)
+      - FIXED #4781: Fixed overflow exceptions in percent-encoding parsing
     - Guidance:
       - CHANGED #4706: Guidance refactoring step to decouple intersection connectivity analysis and turn instructions generation [#4706](https://github.com/Project-OSRM/osrm-backend/pull/4706)
 

src/server/api/url_parser.cpp

@@ -27,7 +27,8 @@ struct URLParser final : qi::grammar<Iterator, Into>
         using boost::spirit::repository::qi::iter_pos;
 
         alpha_numeral = qi::char_("a-zA-Z0-9");
-        percent_encoding = qi::char_('%') > qi::uint_parser<char, 16, 2, 2>()[qi::_val = qi::_1];
+        percent_encoding =
+            qi::char_('%') > qi::uint_parser<unsigned char, 16, 2, 2>()[qi::_val = qi::_1];
         polyline_chars = qi::char_("a-zA-Z0-9_.--[]{}@?|\\~`^") | percent_encoding;
         all_chars = polyline_chars | qi::char_("=,;:&().");