AnalyzerBase: Return base sizeHint() for invalid indices

DetailedErrorDelegate::sizeHint() calls createDetailsWidget() even for
invalid indices, which does not make any sense.

With this change the following messages will not be displayed anymore
when switching to the the Clang Static Analyzer:

    QWidget::setMinimumSize: (/QWidget) Negative sizes (636,-1) are not possible
    QWidget::setMaximumSize: (/QWidget) Negative sizes (636,-1) are not possible

Task-number: QCE-28
Change-Id: I7d45b2625ad94ddccfbb2c22ff5c07ee0bdd1256
Reviewed-by: Robert Loehning <robert.loehning@theqtcompany.com>
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/analyzerbase/detailederrorview.cpp

@@ -51,6 +51,9 @@ DetailedErrorDelegate::DetailedErrorDelegate(QListView *parent)
 QSize DetailedErrorDelegate::sizeHint(const QStyleOptionViewItem &opt,
                                       const QModelIndex &index) const
 {
+    if (!index.isValid())
+        return QStyledItemDelegate::sizeHint(opt, index);
+
     const QListView *view = qobject_cast<const QListView *>(parent());
     const int viewportWidth = view->viewport()->width();
     const bool isSelected = view->selectionModel()->currentIndex() == index;