Fix crash while positioning zero sized table view

TableView expects view size to be specified for loading model items
within it. If not specified, it doesn't load any items (change made
after patch set ebefb583c8).

If user positions the view through positionViewAtCell or
positionViewAtColumn or positionViewAtRow without specifying view size,
then the TableView crashes and its an unexpected behavior.

This patch set adds validation in the TableView to check for loaded
columns or rows during positioning. The document also been updated to
show the expected behavior of TableView when size not specified.

Fixes: QTBUG-113738
Change-Id: Ibd72caada5bfeb290ab5eff3b9ead1e07b3a7176
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit 4bd3738a4e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/quick/items/qquicktableview.cpp

@@ -44,6 +44,12 @@
     using the \l HorizontalHeaderView and \l VerticalHeaderView from
     Qt Quick Controls.
 
+    \note TableView will only \l {isRowLoaded()}{load} as many delegate items as
+    needed to fill up the view. There is no guarantee that items outside the view
+    will be loaded, although TableView will sometimes pre-load items for
+    optimization reasons. Hence, a TableView with zero width or height might not
+    load any delegate items at all.
+
     \section1 Example Usage
 
     \section2 C++ Models
@@ -5640,7 +5646,7 @@ int QQuickTableView::currentColumn() const
 void QQuickTableView::positionViewAtRow(int row, PositionMode mode, qreal offset, const QRectF &subRect)
 {
     Q_D(QQuickTableView);
-    if (row < 0 || row >= rows())
+    if (row < 0 || row >= rows() || d->loadedRows.isEmpty())
         return;
 
     // Note: PositionMode::Contain is from here on translated to (Qt::AlignTop | Qt::AlignBottom).
@@ -5706,7 +5712,7 @@ void QQuickTableView::positionViewAtRow(int row, PositionMode mode, qreal offset
 void QQuickTableView::positionViewAtColumn(int column, PositionMode mode, qreal offset, const QRectF &subRect)
 {
     Q_D(QQuickTableView);
-    if (column < 0 || column >= columns())
+    if (column < 0 || column >= columns() || d->loadedColumns.isEmpty())
         return;
 
     // Note: PositionMode::Contain is from here on translated to (Qt::AlignLeft | Qt::AlignRight).

tests/auto/quick/qquicktableview/data/zerosizedtableview.qml

@@ -15,6 +15,14 @@ Item {
         width: 0
         height: 0
         delegate: tableViewDelegate
+
+        Component.onCompleted: {
+            positionViewAtCell(
+                Qt.point(0,0),
+                TableView.AlignHCenter,
+                Qt.point(-5,-5)
+            );
+        }
     }
 
     Component {