The very first task in a bucket always has the position 0. Now, if we move another task in front of that, it too gets the position 0 assigned. That means the two first tasks now both have the position 0 and are not sorted correctly. This commit fixes that: When moving a task to the very first position it checks if the task now on the second position also has position 0 assigned to it. If that's the case, we'll now update that task's position as well to make sure it has another position than 0.