- fix <rdar://problem/6057650> REGRESSION (r35025): Crash beneath FontCache::invalidate() when activating Safari with no windows open

        * css/CSSFontFaceSource.cpp:
        (WebCore::CSSFontFaceSource::getFontData): Added a null check because
        docLoader() can return 0 now.
        * css/CSSFontSelector.cpp:
        (WebCore::CSSFontSelector::docLoader): Added a null check of m_document.
        (WebCore::CSSFontSelector::addFontFaceRule): Ditto.
        (WebCore::CSSFontSelector::fontLoaded): Ditto.
        (WebCore::CSSFontSelector::fontCacheInvalidated): Ditto.
        (WebCore::fontDataForGenericFamily): Added a null check of document.
        * css/CSSFontSelector.h:
        (WebCore::CSSFontSelector::clearDocument): Added.
        * css/CSSStyleSelector.cpp:
        (WebCore::CSSStyleSelector::~CSSStyleSelector): Added a call to
        CSSFontSelector::clearDocument(). When the style selector is destroyed,
        there is no guarantee that the document will continue to exist.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@35047 268f45cc-cd09-0410-ab3c-d52691b4dbfc