Fix #1768

httplib.h

@@ -2418,6 +2418,7 @@ inline bool is_valid_path(const std::string &path) {
     auto beg = i;
     while (i < path.size() && path[i] != '/') {
       if (path[i] == '\0') { return false; }
+      else if (path[i] == '\\') { return false; }
       i++;
     }