[OT] Insert dotted-circle for run-initial marks

[OT] Insert dotted-circle for run-initial marks

Unfortunately if the font has GPOS and 'mark' feature does
not position mark on dotted-circle, our inserted dotted-circle
will not get the mark repositioned to itself.  Uniscribe cheats
here.

If there is no GPOS however, the fallback positioning kicks in
and sorts this out.

I'm not willing to address the first case.