Merge remote-tracking branch 'upstream/3.4' into merge-3.4

modules/imgproc/src/grabcut.cpp

@@ -175,7 +175,6 @@ void GMM::addSample( int ci, const Vec3d color )
 
 void GMM::endLearning()
 {
-    CV_Assert(totalSampleCount > 0);
     for( int ci = 0; ci < componentsCount; ci++ )
     {
         int n = sampleCounts[ci];
@@ -183,6 +182,7 @@ void GMM::endLearning()
             coefs[ci] = 0;
         else
         {
+            CV_Assert(totalSampleCount > 0);
             double inv_n = 1.0 / n;
             coefs[ci] = (double)n/totalSampleCount;