fix r14062 regression reported by x190 in https://trac.transmissionbt.com/ticket/4076#comment:47

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14064 f4695dd4-2c0a-0410-b89c-da849a56a58e
#5343 slightly better compression in two jQueryUI png files, compressed by Mangix

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14065 f4695dd4-2c0a-0410-b89c-da849a56a58e