Fix a bug which caused crash in SkRTConfig whith string values in environment variables

A minor change to SkRTConfRegistry::parse() fixes this

BUG=skia:1717
R=scroggo@google.com

Review URL: https://codereview.chromium.org/26373008

git-svn-id: http://skia.googlecode.com/svn/trunk@12152 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed