increase iteration count from 16 to 24, when computing cubic-line intersection.
This fixes crbug 170666. Before the fix, were were finishing the "clip" step
with a curve that was still partly negative, and so as assert would fire.

added unittest to confirm that the assert doesn't fire.



git-svn-id: http://skia.googlecode.com/svn/trunk@7278 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed