Check if path exists onOpen.
Changelog entry.
Merge branch 't/10975'
#9929: [Chrome 23] &nbsp; is created when deleting character and typing common space

It seems as &nbsp; is a result of altering source for checkStartOfBlock()/checkEndOfBlock(). Changing order of checks in if checkStartOfBlock()/checkEndOfBlock() are run only when necessary, not every time del/backspace is pressed.