Fix Coverity Scan 1486953 Use after free

plugins/persist-sqlite/base_msgs.c

@@ -115,7 +115,10 @@ static char *properties_to_json(const mosquitto_property *properties)
 			case MQTT_PROP_SERVER_REFERENCE:
 			case MQTT_PROP_REASON_STRING:
 				/* str */
-				mosquitto_property_read_string(properties, propid, &value, false);
+				if(mosquitto_property_read_string(properties, propid, &value, false)){
+					cJSON_Delete(array);
+					return NULL;
+				}
 				if(cJSON_AddStringToObject(obj, "value", value) == NULL){
 					free(value);
 					cJSON_Delete(array);