Merge pull request opencv#19580 from SergeyKrivohatskiy:patch-1

* Fixed OCL implementation of pyrlk

If prevPts size is (N, 1) (which is a default layout for converting `vector<Point2f>` to `UMat`) the `prevPts.cols == 1` and optical flow will be calculated for the first point only.
Getting `prevPts.total()` as in line 1048 is the correct way to get points count.

* fixed compilation warning (size_t to int)

Signed-off-by: Sergey Krivohatskiy <s.krivohatskiy@gmail.com>

Author: SergeyKrivohatskiy

modules/video/src/lkpyramid.cpp

@@ -938,7 +938,8 @@ namespace
             {
                 if (!lkSparse_run(prevPyr[level], nextPyr[level], prevPts,
                                   nextPts, status, err,
-                                  prevPts.cols, level))
+                                  static_cast<int>(prevPts.total()),
+                                  level))
                     return false;
             }
             return true;