fixed handling of shadow tiddlers in SiteIcon view
fixed handling of shadow tiddlers in SiteIcon view

NB: This works around an issue with ImageMacroPlugin, which does not
check whether the data retrieved via its renderImage method is a valid
tiddler object, thus raising a "tiddler is null" exception.

TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace