Fix a sometimes notice in wpmu_current_site()

props johnjamesjacoby. see #27003.
Built from https://develop.svn.wordpress.org/trunk@27275


git-svn-id: http://core.svn.wordpress.org/trunk@27131 1a063a9b-81f0-0310-95a4-ce76da25c4cd
When closing the various "edit" media modals, remove the related views elements from the DOM. Props gcorne, fixes #27204.
Built from https://develop.svn.wordpress.org/trunk@27276


git-svn-id: http://core.svn.wordpress.org/trunk@27132 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Merge remote-tracking branch 'upstream/master'