QIdentityProxyModel: remove slow bounds-checking, for more performance

If we're called out of bounds, sourceModel()->index() will take care of
returning an invalid model index anyway. So calling rowCount+columnCount
every time index() is called can be avoided. These calls can be particularly
slow when sitting on top of a stack of proxymodels. And index() itself is called
very often, i.e. when a proxymodel on top of us is used by a delegate
which calls data() for many different roles.

Change-Id: I00dd5cf432c0591f41e6fa6fc86c845f29845cd1
(cherry picked from qtbase/3de0f442b5857915f26be6600bc8e54d1af08208)
Reviewed-by: Giuseppe D'Angelo <[email protected]>

Author: dfaure-kdab

src/gui/itemviews/qidentityproxymodel.cpp

@@ -162,11 +162,8 @@ QModelIndex QIdentityProxyModel::index(int row, int column, const QModelIndex& p
 {
     Q_ASSERT(parent.isValid() ? parent.model() == this : true);
     Q_D(const QIdentityProxyModel);
-    if (!hasIndex(row, column, parent))
-        return QModelIndex();
     const QModelIndex sourceParent = mapToSource(parent);
     const QModelIndex sourceIndex = d->model->index(row, column, sourceParent);
-    Q_ASSERT(sourceIndex.isValid());
     return mapFromSource(sourceIndex);
 }