Enforce payload_max_length on decompressed size for unframed requests

For a non-SSL request with neither Content-Length nor Transfer-Encoding,
Server::read_content_core() fell back to reading raw wire bytes with
detail::read_content_without_length() directly, bypassing the decompressor
wrapper that the length-framed and chunked paths already use. As a result,
payload_max_length only bounded the compressed bytes read off the socket,
not the decompressed size a handler could produce from them.

Route this fallback through detail::read_content(..., decompress=true)
instead, the same helper already used below for the length-framed and
chunked cases, so the decompressed-size guard applies uniformly.

httplib.h

@@ -12704,15 +12704,12 @@ inline bool Server::read_content_core(
         }
       }
       if (has_data) {
-        auto result =
-            detail::read_content_without_length(strm, payload_max_length_, out);
-        if (result == detail::ReadContentResult::PayloadTooLarge) {
-          res.status = StatusCode::PayloadTooLarge_413;
-          return false;
-        } else if (result != detail::ReadContentResult::Success) {
-          return false;
-        }
-        return true;
+        // Route through the same decompressing reader used by the
+        // length-framed and chunked paths below, so payload_max_length_ is
+        // enforced on the decompressed size here too instead of only on the
+        // compressed wire bytes.
+        return detail::read_content(strm, req, payload_max_length_, res.status,
+                                    nullptr, out, true);
       }
     }
     return true;