Don't let avatar image in Extended Profile dashboard panel exceed container width

This could become a problem when themes are using a blanket declaration to
change the default avatar width on the front end.

Fixes #5486

Props Bowromir

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8246 cdf35c40-ae34-48e0-9cc9-0c9da1808c22