Make SkMatrix44::invert() check for finite 1/det instead of magic value

Make SkMatrix44::invert() check for finite 1/det instead of magic value

Previously we were checking to see if the magnitude of determinant of the
matrix to be inverted was less than 1.0e-8, which is a magic number possibly
plucked from Graphics Gems. After some discussion, it's been determined (ha)
that we can simply check to see if 1/det is finite and if so proceed.

BUG=222926
R=reed@google.com, shawnsingh@chromium.org

Author: jvanverth@google.com

Review URL: https://chromiumcodereview.appspot.com/22904003

git-svn-id: http://skia.googlecode.com/svn/trunk@10758 2bbb7eff-a529-9590-31e7-b0007b416f81