Fix [#37409] Missing Buttons in Edit Strip Sub-Menu for Sound Strips in the VSE

Add back mute & lock buttons to audio strips (these should not have been removed, own fault).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61234 954f8c5b-7b00-dc11-b283-0030488c597c