Node does not get updated in case QSGGeometry::allocate() is called with the same value as before

Steps to reproduce (hope I did not forget anything):

1. create a QSGGeometry with a certain vertexCount and indexCount.
2. Fill the vertices with data.
3. Assign the geometry to a node and let it render.

4. Then call QSGGeometry::allocate() with the same vertexCount and indexCount.
5. Modify the data.
6. mark the node's geometry as dirty: node->markDirty(QSGNode::DirtyGeometry);

Result: The updated node is not rendered.

Workaround: insert QSGGeometry::allocate(1); between steps 3 and 4 to force a reallocation in step 4.