Cancelling MongoDB query operation causes Parse Server crash

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

Cancelling a query operation in MongoDB causes Parse Server to crash.
This is not a security vulnerability as access to the DB server is required.

Steps to reproduce

1. Send a request from Parse Server with a long-running query.
2. On the MongoDB server side, terminate the ongoing query operation. This may need to be repeated several times as a retry is usually issued and the terminated operation will be restarted.
3. Parse Server crashes and rends a with 5xx response to the client.

Actual Outcome

Parse Server crashes.

Expected Outcome

Parse Server should not crash but send an appropriate error code to the client.

Environment

Server

• Parse Server version: 5.5.1, likely that this also affects 6.x
• MongoDB version: 4.2.24

Start by reproducing the cancelled long-running query with Parse Server 5.5.1 and MongoDB 4.2.24, repeating the termination as described to observe the retry and crash path. Trace the resulting MongoDB error through the Parse Server request handling, then verify that cancellation returns an appropriate 5xx response without crashing the server.