QAIV drop indicator: don't draw a single pixel when the rect is null

Drive-by change: fix a trivial typo
Also, clang-format changed some indentation

Fixes: QTBUG-36831
Change-Id: Icb259cc8a1fc83aca3d4cd581fa0e88e7907602b
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit 39e7016)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/itemviews/qabstractitemview.cpp

@@ -3415,7 +3415,7 @@ void QAbstractItemView::dataChanged(const QModelIndex &topLeft, const QModelInde
             }
         }
         if (isVisible() && !d->delayedPendingLayout) {
-            // otherwise the items will be update later anyway
+            // otherwise the items will be updated later anyway
             update(topLeft);
         }
     } else {

src/widgets/itemviews/qabstractitemview_p.h

@@ -164,10 +164,11 @@ class Q_AUTOTEST_EXPORT QAbstractItemViewPrivate : public QAbstractScrollAreaPri
     inline void paintDropIndicator(QPainter *painter)
     {
         if (showDropIndicator && state == QAbstractItemView::DraggingState
+            && !dropIndicatorRect.isNull()
 #ifndef QT_NO_CURSOR
             && viewport->cursor().shape() != Qt::ForbiddenCursor
 #endif
-            ) {
+        ) {
             QStyleOption opt;
             opt.initFrom(q_func());
             opt.rect = dropIndicatorRect;