Crashes at loadBookmarks if bookmarks are never saved before

[hinzberg]

If the bookmarks are never saved before you should not force unwrap them.
I fixed it like this.

func loadBookmarks()
{
let path = getBookmarkPath()

let bookmarksTemp = NSKeyedUnarchiver.unarchiveObject(withFile: path) as? [URL: Data]
if bookmarksTemp != nil {
    bookmarks = bookmarksTemp!
    for bookmark in bookmarks
    {
        restoreBookmark(bookmark)
    }
}

}