Editing MR Cancel button redirects to issue of same ID

1. Open an MR.
2. Click Edit
3. Click Cancel.

ER: takes you back to said MR
AR: takes you to an issue of that ID.

mentioned in issue #14303 (closed)

AR: …or to a 404, when no such issue exists.

This is already fixed on !3392 (merged) and !3417 (merged)

Closing.

Status changed to closed