Calling clear_mapping causes the persistent indexes to be queried, and
mapped using map_to_source, so that they can be restored later. That
is not the appropriate response to the source model being deleted
because there won't be anything to restore.
Simply clear the stored mapping information instead so that the source model
actually exists when mapToSource is called by the framework.
Change-Id: I99692ee7aa9c6714aec45c68fe4a2d62be189d60
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
722798a359