The fix for #718 missed the need for dequeuing the next coroutine after canceling an obsolete coroutine.

The next coroutine will still eventually get dequeued, but not for about 15 seconds.

Sample Repro

Steps:

1. Have a prompt script installed which uses clink.promptcoroutine() to run git commands in the background while in a git repo directory.
2. Verify that the prompt script shows visible feedback while it's waiting on background commands.
3. Press Enter, and then press Enter immediately after the first press. The second press must happen before the prompt's background git command(s) finish.

Expected Result:

As soon as the background command completes (usually in just a second or two), the display should switch to something like this:

Actual Result:

This kind of display can linger for about 15 seconds: