… cursor in some situations

This would happen in this situation:
* The user hovers an element, whose tooltip is too big for the available
  space: the tooltip would align with the window's left edge.
* Then the user hovers another element whose tooltip would have space to
  go either at the right or left of the cursor. In that case we reuse the
  previous position, so that the tooltip stays stable.
  But if the previous position was the window-edge, then the tooltip
  would stay at that location and could be far from the mouse cursor.

…-to-another-position