Update httplib.h

Co-authored-by: Copilot <[email protected]>

Author: yhirose

httplib.h

@@ -8458,8 +8458,10 @@ inline bool Server::check_if_not_modified(const Request &req, Response &res,
       // simplified implementation requires exact matches.
       auto ret = detail::split_find(val.data(), val.data() + val.size(), ',',
                                     [&](const char *b, const char *e) {
-                                      auto tag = std::string(b, e);
-                                      return tag == "*" || tag == etag;
+                                      auto len = static_cast<size_t>(e - b);
+                                      if (len == 1 && *b == '*') return true;
+                                      if (len == etag.size() && std::equal(b, e, etag.begin())) return true;
+                                      return false;
                                     });
 
       if (ret) {