Fixed potential crash if applying console style caused new messages to be logged.
As UIElement::GetAppliedStyle() returns an empty string for the 'auto' style, also allow to use SetStyle() with empty string to apply the auto style.


git-svn-id: http://urho3d.googlecode.com/svn/trunk@2521 3bd170d8-ddcf-f82c-f583-7a401ccf5608