GH-2704 - Always define __relationships__ parameter.

In #2668 storing of relationships has been optimised so that existing relationships are not always refetched. The new query always requires `__relationships__` to be present. In the case of relationships with defined properties, `Neo4jMappingContext#createStatementForRelationshipWithPropertiesBatch` only defines that argument for new relationships, so updating relationships with properties fails.

Closes #2704

Author: michael-simons

src/main/java/org/springframework/data/neo4j/core/mapping/Neo4jMappingContext.java

@@ -614,8 +614,8 @@ private CreateRelationshipStatementHolder createStatementForRelationshipWithProp
 				getEntityConverter().write(relatedValue.getRelationshipProperties(), propMap);
 				relationshipRows.add(propMap);
 			}
-			relationshipPropertiesEntries.put(Constants.NAME_OF_RELATIONSHIP_LIST_PARAM, relationshipRows);
 		}
+		relationshipPropertiesEntries.put(Constants.NAME_OF_RELATIONSHIP_LIST_PARAM, relationshipRows);
 		return new CreateRelationshipStatementHolder(relationshipCreationQuery, relationshipPropertiesEntries);
 	}