Pisces / Marlin Strokers may generate invalid curves with huge coordinates and round joins

In both Pisces & Marlin, the Stroker may generate invalid round joins with huge coordinates that may cause rendering artefacts.

See http://mail.openjdk.java.net/pipermail/graphics-rasterizer-dev/2015-December/000421.html

The problem is in the Stroker.drawBezApproxForArc()
method (from Pisces):
cv = NaN because sqrt(0.5 - cosext2) = NaN if cosext2 > 0.5 !

It happens when floating-point rounding errors lead to cosext2 > 0.5 !

After discussion with Jim Graham, the proper fix is very simple:

        // check cos(ext) <= 1 to avoid cv = NaN:
        if (cosext2 > 0.5f) {
            // just return to avoid generating a flat curve:
            return;
        }

This impacts all renderers derived from OpenJDK Pisces (since java 1.6 ?) ie Marlin but maybe also OpenPisces.