Don't crash when adding function calls that return multiple results.
Don't crash when adding function calls that return multiple results.

R=iant
CC=gofrontend-dev
https://golang.org/cl/3816046

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