backport: on document closing, clear the fifo with allocated text pages

(fixes potential crash because of references to potentially non-existing pages in the next open document)

svn path=/branches/KDE/4.2/kdegraphics/okular/; revision=923021

core/document.cpp

@@ -1813,6 +1813,7 @@ void Document::closeDocument()
     d->m_viewportHistory.append( DocumentViewport() );
     d->m_viewportIterator = d->m_viewportHistory.begin();
     d->m_allocatedPixmapsTotalMemory = 0;
+    d->m_allocatedTextPagesFifo.clear();
     d->m_pageSize = PageSize();
     d->m_pageSizes.clear();
     AudioPlayer::instance()->d->m_currentDocument = KUrl();