[PDF] Handle failures of matrix inversion

Previously reviewed in https://codereview.appspot.com/6033047.  Rolled back
because of unrelated fixed-point bugs.

Review URL: https://codereview.appspot.com/6052051

git-svn-id: http://skia.googlecode.com/svn/trunk@3715 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed