fix: add nullcheck for legacy speed settings

[SammCheese]

Description

A bug in my PR (#1413) led to erroneous behavior when the transfer speed was 0 (unlimited) as pointed out by @shatyuka here.
This PR adds a check for this and falls back to K for this case.

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran app with your changes locally?