letterrip: Fix blank-letter to work even if letter selection is cancelled

letterrip: Fix blank-letter to work even if letter selection is cancelled

If a user is moving a blank tile off of their rack onto the board,
then they are required to choose a letter for the blank. In this
situation, cancelling letter selection cause the blank tile to be
returned to the rack.

In contrast, when moving a blank tile from one space on the board to
the other, the blank will already have a selected letter, and it's
reasonable for that selection to be unchanged. So in this case,
cancelling the letter selection should let the movement work, and
should not send the letter back to the rack.

This commit fixes that scenario by performing the movement prior to
bringing up the selection modal. That way, if the selection modal is
cancelled, there's nothing else to do and the user gets the desired
behavior (the tile moved, unchanged).