When there is no material library node, material library presence should be ensured before attempting to create a new material

New material can be created in various ways:

• Dragging new material from library to navigator
• Dragging new model from library to navigator or 3D editor
• Dragging new View3D from library to form editor or navigator

All these should trigger equivalent of MaterialEditorView::ensureMaterialLibraryNode(), and preferably in the same transaction as the triggering action.