When this happens, fYHead (the end of the topcap) will be greater
than fYTail (the start of the bottomcap). We want to clip rendering
of one of them, so we don't draw them both in the same spot. However,
we're clipping both of them: the topcap to the bottomcap's actual start
and the bottomcap to the topcap's actual end. This leaves a gap between
them. Only clip the bottomcap.
Glenn Maynard
1a63e18756