added to DetectorExtractor test the check of compute() on empty data. Added test for BRIEF.

modules/features2d/include/opencv2/features2d/features2d.hpp

@@ -2109,8 +2109,7 @@ inline void BruteForceMatcher<Distance>::commonKnnMatchImpl( BruteForceMatcher<D
      size_t imgCount = matcher.trainDescCollection.size();
      vector<Mat> allDists( imgCount ); // distances between one query descriptor and all train descriptors
      for( size_t i = 0; i < imgCount; i++ )
-		 if( matcher.trainDescCollection[i].rows )
-			allDists[i] = Mat( 1, matcher.trainDescCollection[i].rows, DataType<DistanceType>::type );
+        allDists[i] = Mat( 1, matcher.trainDescCollection[i].rows, DataType<DistanceType>::type );
 
      for( int qIdx = 0; qIdx < queryDescriptors.rows; qIdx++ )
      {

modules/features2d/src/descriptors.cpp

@@ -358,7 +358,7 @@ Ptr<DescriptorExtractor> createDescriptorExtractor(const string& descriptorExtra
   }
   else if (!descriptorExtractorType.compare("BRIEF"))
   {
-    de = new BriefDescriptorExtractor(32);
+    de = new BriefDescriptorExtractor();
   }
   return de;
 }