Fix UI for choosing a profile picture when user has no picture

Summary: Currently, we always show "current picture" even if you don't have one. In this case, the first available picture becomes the "current picture". Instead, show "current picture" only if there's actually a current picture to show.

Test Plan: {F49875}

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6432