Fixed scrolling performance issue related to hidden blocks
Fixed scrolling performance issue related to hidden blocks

Due to a wrong lookup (confusing line and block number) the scroll
optimization was broken, causing the entire view to be updated.

Reviewed-by: Thorbjørn Lindeijer

RLovelett/qt,pruiz/wkhtmltopdf-qt,radekp/qt,RLovelett/qt,igor-sfdc/qt-wk,radekp/qt,KDE/qt,KDE/qt,radekp/qt,KDE/qt,KDE/qt,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,KDE/qt,RLovelett/qt,radekp/qt,RLovelett/qt,igor-sfdc/qt-wk,RLovelett/qt,KDE/qt,RLovelett/qt,radekp/qt,radekp/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,radekp/qt,RLovelett/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,KDE/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,KDE/qt,RLovelett/qt,igor-sfdc/qt-wk,RLovelett/qt,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt