Don't crash checking for unexported self-referential pointer field.
Don't crash checking for unexported self-referential pointer field.

R=iant
CC=gofrontend-dev
https://golang.org/cl/4185043

anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend