Asana \underbrace doesn't appear in WebKit

The \underbrace doesn't show up in the Asana font in WebKit.

It appears there is a clipping bug in WebKit that is behind this. It may be that if the clipping region lies outside the usual height and depth of the line, that WebKit doesn't draw the glyphs, even though they should be draw.

A work around would be for MathJax to alter its clip region, but I'm not sure exactly what the parameters controlling the bug are. It would probably be safe to allow the height of the clipping region to be forced to 0 if it is negative so that it does not go below the baseline.