Fix FeaturesMatcher collection keypoints

Author: shimat

src/OpenCvSharp/Modules/stitching/FeaturesMatcher.cs

@@ -102,7 +102,7 @@ public virtual MatchesInfo[] Apply(
                     throw new ArgumentException("features contain null descriptor mat", nameof(features));
                 featuresArray[i].Descriptors.ThrowIfDisposed();
 
-                keypointVecs[i] = new StdVector<KeyPoint>();
+                keypointVecs[i] = new StdVector<KeyPoint>(featuresArray[i].Keypoints);
                 wImageFeatures[i] = new WImageFeatures
                 {
                     ImgIdx = featuresArray[i].ImgIdx,

test/OpenCvSharp.Tests/stitching/FeaturesMatcherTest.cs

@@ -46,9 +46,8 @@ public void ApplyMultipleImageFeatures()
         using var source = LoadImage("lenna.png", ImreadModes.Grayscale);
         var images = new[]
         {
-            source[new Rect(0, 0, 200, 200)].Clone(),
-            source[new Rect(100, 100, 200, 200)].Clone(),
-            source[new Rect(200, 0, 200, 200)].Clone(),
+            source.Clone(),
+            source.Clone(),
         };
         try
         {
@@ -71,6 +70,12 @@ source[new Rect(200, 0, 200, 200)].Clone(),
                     Assert.InRange(m.DstImgIdx, -1, images.Length - 1);
                 }
 
+                var forwardMatch = Assert.Single(
+                    matches, m => m.SrcImgIdx == 0 && m.DstImgIdx == 1);
+                Assert.NotEmpty(forwardMatch.Matches);
+                Assert.True(forwardMatch.NumInliers > 0);
+                Assert.False(forwardMatch.H.Empty());
+
                 foreach (var m in matches)
                     m.Dispose();
             }