Reviewed by Darin.

    Reviewed by Darin.

        Fix for <rdar://problem/3993628> REGRESSION (180-181): Logitelnet bank's website doesn't work

        This fixes an oversight in the fix for <rdar://problem/3964286>.
        We're now making sure there is a document before calling checkCompleted in slotLoaderRequestDone.
       	That function is called even when other parts finish loads of their subresources, so we could end
	up calling checkCompleted before we had a document. We also looked over all the other calls to
	checkCompleted to convince ourselves no other call sites had a similar issue.

        * khtml/khtml_part.cpp: (KHTMLPart::slotLoaderRequestDone): Check if doc is nil before calling
	checkCompleted.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@8539 268f45cc-cd09-0410-ab3c-d52691b4dbfc