Ensure one can add tablespaces on an upgraded cluster

The "tablespaceMounts" portion of the CR would be "null" on an
upgrade, which in turn would cause the unmarshaled map to be
"nil". By initializing the map when a tablespace is being added
to a cluster that was ugpraded from an earlier version of the
PostgreSQL Operator, one can ensure successful addition and
execution.

Author: Jonathan S. Katz

apiserver/clusterservice/clusterimpl.go

@@ -1764,6 +1764,12 @@ func UpdateCluster(request *msgs.UpdateClusterRequest) msgs.UpdateClusterRespons
 			cluster.Spec.EnableBackrestMemoryLimit = false
 		}
 
+		// if TablespaceMounts happens to be nil (e.g. an upgraded cluster), and
+		// the tablespaces are being updated, set it here
+		if len(request.Tablespaces) > 0 && cluster.Spec.TablespaceMounts == nil {
+			cluster.Spec.TablespaceMounts = map[string]crv1.PgStorageSpec{}
+		}
+
 		// extract the parameters for the TablespaceMounts and put them in the
 		// format that is required by the pgcluster CRD
 		for _, tablespace := range request.Tablespaces {