Update indentation to match rest of file

Very cosmetic, but was analyzing code and just wanted to make it
consistent.

modules/features2d/src/matchers.cpp

@@ -540,8 +540,10 @@ void DescriptorMatcher::add( InputArrayOfArrays _descriptors )
         trainDescCollection.insert( trainDescCollection.end(), descriptors.begin(), descriptors.end() );
     }
     else
+    {
         CV_Assert( _descriptors.isUMat() || _descriptors.isUMatVector() || _descriptors.isMat() || _descriptors.isMatVector() );
     }
+}
 
 const std::vector<Mat>& DescriptorMatcher::getTrainDescriptors() const
 {