Deleting tags can leave the cursor unreachable

[roberthchapman]

1. enter a few tags then start typing a new tag
2. scroll left so the text goes off-screen
3. delete a couple of tags but not enough to let the text come back on screen
4. scroll back to the right
   Then the cursor position is not updated correctly and can be off screen and unreachable (and continuing can then cause a crash).

The solution is it just needs the cursor to be moved left by the width of the deleted tag each time a tag is deleted.

Rob