don't run if <map> has no <area>

[vladkras]

In one of my projects

Maybe add some default option like 'emptyMap': true for backward compatibility, so it could be disabled on startup if desired.

Possible solution:

// if map has no descendant areas and option is set to false
if (!map.has('area').length && !option.emptyMap) {
    return
}

somewhere near line 235 of http://davidlynch.org/projects/maphilight/jquery.maphilight.js