Heat Task Stuck errors in RRF 3.6.2-beta.1

[dc42]

See https://forum.duet3d.com/topic/38842/can-problems-since-3-6-1/17 and subsequent posts. Analysis of the main board M122 reports suggests that the Move task may be looping indefinitely. The stack traces place the Move task in DDARing::Spin and in DDA::GetTimeLeft (which is called by DDARing::Spin). Not reproduced by Duet3d but the person reporting the issue has had it happen multiple times.

[dc42]

This likely has the same cause as #1200 because the function will loop indefinitely if all DDAs in the ring have state Committed. The fix for that issue should fix this one also. The user reporting this issue has been asked to try the build containing that fix.