Fix a memory leak in node_cells_free_memory.
Fix a memory leak in node_cells_free_memory.

The leak could occur if either the start or the max
cells was an invalid type.

Signed-off-by: Chris Lalancette <60b62644009db6b194cc0445b64e9b27bb26433a@redhat.com>

libvirt/ruby-libvirt,libvirt/ruby-libvirt,libvirt/ruby-libvirt