todo.sh >= 2.0 leaves blank lines on task deletion

Todo.sh, v2.0 onwards introduces blank lines in the todo.txt file in case a task is deleted.  This messes up the display of workflow in Alfred, with a bunch of "1:" tasks which will throw an error on any action.  My change is tiny -- it strips out blank lines before processing.

Have also updated the "todotxt.alfredworkflow" file too, though I'm not sure if you want that.