[path-bar] Use the correct value for height
[path-bar] Use the correct value for height

Make sure to take away padding from the for_height value when getting
the preferred width of a crumb. As there's no padding in the default
style, this bug wasn't being exposed.

jonnylamb/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,pwithnall/mx,pwithnall/mx