Fix JSON::GeneratorError masking errors for malformed UTF-8 request bodies

[grk]

Problem

Rollbar::RequestDataExtractor#extract_request_data_from_rack serializes the parsed raw body params to JSON while building the :body field:

:body => Rollbar::JSON.dump(raw_body_params),

This serialization happens before the payload-wide UTF-8 normalization pass that Rollbar::Item runs (Rollbar::Util.enforce_valid_utf8). When a request body contains invalid UTF-8 — for example a malformed request that Rails rejects with ActionController::BadRequest — Rollbar::JSON.dump raises JSON::GeneratorError: source sequence is illegal/malformed utf-8.

The result is that the original exception being reported gets replaced with a failsafe report, masking the real error (ActionController::BadRequest) from users.

Fix

Normalize the parsed body params with Rollbar::Util.enforce_valid_utf8 inside mergeable_raw_body_params, before they are scrubbed and serialized. This mirrors the existing payload-wide UTF-8 handling and ensures the :body field can always be serialized, so the original error is reported correctly.

The change is limited to error-report payload content; request parsing/validation is unaffected.

Test

Added a spec that feeds a JSON POST body with an invalid UTF-8 byte through extract_request_data_from_rack. Without the fix it raises JSON::GeneratorError; with the fix it returns a valid, UTF-8 :body string.