QNetworkAccessManager: do not segfault when using a network cache
QNetworkAccessManager: do not segfault when using a network cache

Don't setfault when setting 0 for the network cache such as when you
want to disable it.

    Reviewed-by: Peter Hartmann

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