[okular] [Bug 415340] Crash when closing print preview dialog on Linux

[jimbo1qaz]

https://bugs.kde.org/show_bug.cgi?id=415340

--- Comment #2 from jimbo1qaz <jimbo1qaz at protonmail.com> ---
The crash occurs after ~FilePrinterPreview finishes, while unwinding
FilePrinterPreview's Qt child widgets (via QObjectPrivate::deleteChildren).

Okular::Part::~Part calls Okular::Document::closeDocument calls
d->saveDocumentInfo().

void DocumentPrivate::saveDocumentInfo() const
{
    ...
    for ( View *view : qAsConst(m_views) )
    {
        QDomElement viewEntry = doc.createElement( QStringLiteral("view") );
        viewEntry.setAttribute( QStringLiteral("name"), view->name() );
        viewsNode.appendChild( viewEntry );
        saveViewsInfo( view, viewEntry );
    }


void DocumentPrivate::saveViewsInfo( View *view, QDomElement &e ) const
{
    ...
        const bool mode = view->capability( View::Continuous ).toBool();

QVariant PageView::capability( ViewCapability capability ) const
{
    switch ( capability )
    {
        ...
        case Continuous:
            return d->aViewContinuous->isChecked();

## Null pointers

The problem is that PageView::d's member pointers are mostly nullptr (assigned
by the constructor). This is what causes the crash.

Is the PageViewPrivate of a print preview document supposed to contain many
nullptr, or should the pointers be initialized through
PageView::setupViewerActions()? (This method constructs QAction and whatnot.
Maybe it makes no sense to initialize them to QAction/etc, since the print
preview dialog has no buttons.)

## Operating on null pointers.

I'm suspicious that Okular::Document::closeDocument unconditionally calls
DocumentPrivate::saveDocumentInfo() (which leads to the crash). Is it necessary
to save the info of a print-preview document? (It crashes if
PageView::setupViewerActions() has not been called.)

The hacky workaround is to patch PageView::capability() to return some dummy
value instead of dereferencing null pointers.

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