QAIM: return false if nothing was (or could be) done in setItemData

Setting item data on an invalid index, or with an empty map, surely is
not a successful operation.

[ChangeLog][Core][QAbstractItemModel] Calling setItemData with an
invalid index or empty map of data returns false.

Change-Id: Id087581243c8fa39a8cc78b811ecd087deea4466
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/itemmodels/qabstractitemmodel.cpp

@@ -2086,6 +2086,9 @@ bool QAbstractItemModel::clearItemData(const QModelIndex &index)
 */
 bool QAbstractItemModel::setItemData(const QModelIndex &index, const QMap<int, QVariant> &roles)
 {
+    if (!index.isValid() || roles.isEmpty())
+        return false;
+
     // ### TODO: Consider change the semantics of this function,
     // or deprecating/removing it altogether.
     //