Clear invalid field maps in PropertyAccessInfo.

BUG=363956
TEST=mjsunit/regress/regress-363956
LOG=y
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/239623005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20788 ce2b1a6d-e550-0410-aec6-3dcde31c8c00