Reviewed by Adele.

    Reviewed by Adele.

        - fixed <rdar://problem/4023337> Safari stops loading any page (-[NSCFDictionary setObject:forKey:]:
        attempt to insert nil key)

        It is very likely that the exception being hit is caused by the same problem as WebFoundation
        bug 4018486. This change makes the code robust against this kind of problem regardless.

        * WebView.subproj/WebBaseResourceHandleDelegate.m:
        (-[WebBaseResourceHandleDelegate saveResource]):
        Don't call addSubresource if newly-created resource is nil (but do assert on debug builds).
        Also assert that originalURL and MIMEType are not nil.

        * WebView.subproj/WebDataSource.m:
        (-[WebDataSource addSubresource:]):
        Don't add nil subresource to dictionary, but do assert on debug builds.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@8755 268f45cc-cd09-0410-ab3c-d52691b4dbfc