Pearl: permit drawing a whole loop in one drag.

A user reported recently that they were trying this as an extra
challenge (solve the whole puzzle mentally and then draw it in
finished form in one UI action). But the backtracking behaviour of
Pearl's dragging mode meant that the loop erased itself as soon as the
drag came back to a revisited position.

In this commit I fix that by making the exception that you can
unconditionally return to the start point of the drag, _provided_ that
in doing so you don't create a grid cell of degree > 2.

0 files changed, 0 insertions, 0 deletions