No panic, we reeally insert dotted circle when it's absolutely broken.

Fixes most of the dotted-circle cases against Uniscribe. (for Devanagari
fixes 80% of them, for Khmer 70%; the rest look like Uniscribe being
really bogus...)

I had to make a decision.  Apparently Uniscribe adds one dotted circle
to each broken character.  I tried that, but that goes wrong easily with
split matras.  So I made it add only one dotted circle to an entire
broken syllable tail.  As in: "if there was a dotted circle here, this
would have formed a correct cluster."  That works better for split
stuff, and I like it more.