On error in onUserQuery, send back specific HTTP status and errorcode

[tak-hntlabs]

Describe the bug
I am building an appservice. The AppService.onGetUsers returns http status 200 in the response message when an exception has occurred this.onUserQuery. Specifically, the onGetUsers method catches the exception, but does this:

// AppService.ts line 232
} catch (e) { res.send({ ... }); }.

This call sends back http status 200. The 200 status is surprising. I had expected 4xx for any exceptions or error because the request is not successful. Consequently, on the dendrite server, the rest of the logic mistakenly assumes the user query succeeded and eventually runs into other issues.

To Reproduce
Dev repro:

1. Set up Dendrite server + appservice.
2. Throw an exception in the implementation of onUserQuery.

Expected behavior
The catch block should return a 4xx status.

[Half-Shot]

Marking as a defect because we should be handling errors properly.

[Half-Shot]

Fixed by #422. Thank you @tak-hntlabs !