Loop insertion marker can't move from "around" to "previous" and vice-versa

[drigz]

If you drag a pants block over another block, then try to drag it left so that it's before the other block, the insertion marker won't move until you drag away and return. This is nothing severe but slightly clunky.

dragging left with the issue

The expected behaviour can be achieved by patching updatePreviews to recognise an insertion marker as invalid if localConnection has changed, not just if highlightedConnection has changed.

expected behaviour

I tried to fix this with #252, which caused #263, so I reverted the change.

[tmickel]

This is odd, yeah. Thanks for the new issue!