dom0/qmemman: fix reporting to qubes-manager
dom0/qmemman: fix reporting to qubes-manager

When VM is shutting down, xenstore entries (especially 'name') can be deleted
before qmemman remove VM from its list. So check if name is defined before
reporting to qubes-manager.

marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin