TRAC #12184
This is necessary because a NaN generated in flattened conditional code fails to get discarded on certain devices.
Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

Author:    Nicolas Capens

git-svn-id: https://angleproject.googlecode.com/svn/trunk@248 736b8ea6-26fd-11df-bfd4-992fa37f6226