storage/lvm: don't try to resize non-existing lvm volumes
storage/lvm: don't try to resize non-existing lvm volumes

Volume with save_on_stop=False and snap_on_start=False exists only when
VM is running and this is already handled under is_dirty() condition.
For non-running VMs, skip LVM resize step and only update internal size
attribute.

Fixes QubesOS/qubes-issues#5645

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