Update spf.dom.classlist to handle empty strings safely.
Update spf.dom.classlist to handle empty strings safely.

Progress on #299.

scrapp-uk/spfjs,youtube/spfjs,tchiotludo/spfjs,nicksay/spfjs,theanh/spfjs,youtube/spfjs,youtube/spfjs,nicksay/spfjs,theanh/spfjs,theanh/spfjs,tchiotludo/spfjs,tchiotludo/spfjs,scrapp-uk/spfjs,theanh/spfjs,tchiotludo/spfjs,youtube/spfjs,scrapp-uk/spfjs,youtube/spfjs,scrapp-uk/spfjs,nicksay/spfjs,scrapp-uk/spfjs,nicksay/spfjs,tchiotludo/spfjs,nicksay/spfjs,theanh/spfjs