Определить, является ли объект points пустым
BRISKPoints | cornerPoints | detectBRISKFeatures | detectFASTFeatures | detectHarrisFeatures | detectKAZEFeatures | detectMinEigenFeatures | detectMSERFeatures | detectORBFeatures | detectSURFFeatures | extractFeatures | KAZEPoints | matchFeatures | MSERRegions | ORBPoints | SURFPoints