fix initial values bug

modules/stitching/src/matchers.cpp

@@ -543,6 +543,7 @@ void FeaturesMatcher::operator ()(const vector<ImageFeatures> &features, vector<
             if (features[i].keypoints.size() > 0 && features[j].keypoints.size() > 0 && mask_(i, j))
                 near_pairs.push_back(make_pair(i, j));
 
+    pairwise_matches.clear(); // clear history values
     pairwise_matches.resize(num_images * num_images);
     MatchPairsBody body(*this, features, pairwise_matches, near_pairs);