ceph: prevent operator crash with host networking and mon not found

When the node is not found for mon assignment with host networking
enabled, the operator may crash. This change ensures the node is
not nil and returns an error instead of crashing.

Signed-off-by: Travis Nielsen <tnielsen@redhat.com>

pkg/operator/ceph/cluster/mon/mon.go

@@ -789,8 +789,8 @@ func (c *Cluster) initMonIPs(mons []*monConfig) error {
 		if c.spec.Network.IsHost() {
 			logger.Infof("setting mon endpoints for hostnetwork mode")
 			node, ok := c.mapping.Schedule[m.DaemonName]
-			if !ok {
-				return errors.New("mon doesn't exist in assignment map")
+			if !ok || node == nil {
+				return fmt.Errorf("node for mon %q doesn't exist in assignment map", m.DaemonName)
 			}
 			m.PublicIP = node.Address
 		} else {