Use schema var in createCollection instead of ref

Just reduces the number of references for now, this function will need splitting later.

db/collection.go

@@ -137,9 +137,10 @@ func (db *db) createCollection(
 		return nil, err
 	}
 
+	schema := col.desc.Schema
 	// Local elements such as secondary indexes should be excluded
 	// from the (global) schemaId.
-	schemaBuf, err := json.Marshal(col.desc.Schema)
+	schemaBuf, err := json.Marshal(schema)
 	if err != nil {
 		return nil, err
 	}
@@ -155,8 +156,9 @@ func (db *db) createCollection(
 	// For new schemas the initial version id will match the schema id
 	schemaVersionID := schemaID
 
-	col.desc.Schema.VersionID = schemaVersionID
-	col.desc.Schema.SchemaID = schemaID
+	schema.VersionID = schemaVersionID
+	schema.SchemaID = schemaID
+	col.desc.Schema = schema
 
 	// buffer must include all the ids, as it is saved and loaded from the store later.
 	buf, err := json.Marshal(col.desc)