Fixing issue #2864

If you call element.attr ('style') with Zepto and
there is NO inline style, you get back the
CSS2Properties object. In jQuery you would get
nothing.

To avoid calling split in an object instead of a
string we should check if we really have a string.

Signed-off-by: Leo Unglaub <leo@leo-unglaub.net>
Merge pull request #2866 from LeoUnglaub/master

Fixing issue #2864