QGraphicsSceneBspTreeIndex: fix misleading code in event()

The old code employed a switch statement to filter timer events,
but fell unconditionally through to the default case of calling
QObject::event(). The final return statement following the switch
is thus dead code.

Fix by turning the switch into an if and returning QObject::event()
unconditionally afterwards, which much better describes the intent
of the code, and also fixes the GCC 7 warning about implicit fall-
through in the switch (which wasn't implicit to a human, but GCC's
comment-reading-capabilities are somewhat limited at this point).

Change-Id: I6756a65b3679a446d09fd721dfd0adc24fdf7772
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp

@@ -691,8 +691,7 @@ void QGraphicsSceneBspTreeIndex::itemChange(const QGraphicsItem *item, QGraphics
 bool QGraphicsSceneBspTreeIndex::event(QEvent *event)
 {
     Q_D(QGraphicsSceneBspTreeIndex);
-    switch (event->type()) {
-    case QEvent::Timer:
+    if (event->type() == QEvent::Timer) {
             if (d->indexTimerId && static_cast<QTimerEvent *>(event)->timerId() == d->indexTimerId) {
                 if (d->restartIndexTimer) {
                     d->restartIndexTimer = false;
@@ -701,11 +700,8 @@ bool QGraphicsSceneBspTreeIndex::event(QEvent *event)
                     d->_q_updateIndex();
                 }
             }
-     // Fallthrough intended - support timers in subclasses.
-    default:
-        return QObject::event(event);
     }
-    return true;
+    return QObject::event(event);
 }
 
 QT_END_NAMESPACE