calib3d: fix build warnings

modules/calib3d/src/chessboard.cpp

@@ -2557,6 +2557,7 @@ std::vector<cv::Point2f> Chessboard::Board::getContour()const
                 last = 1;
                 break;
             }
+            /* fallthrough */
         case 2: // right
             if(iter.right(true))
             {
@@ -2566,6 +2567,7 @@ std::vector<cv::Point2f> Chessboard::Board::getContour()const
                 last = 2;
                 break;
             }
+            /* fallthrough */
         case 3: // bottom
             if(iter.bottom(true))
             {
@@ -2575,6 +2577,7 @@ std::vector<cv::Point2f> Chessboard::Board::getContour()const
                 last = 3;
                 break;
             }
+            /* fallthrough */
         case 4: // left
             if(iter.left(true))
             {

modules/calib3d/test/test_chesscorners.cpp

@@ -148,6 +148,7 @@ void CV_ChessboardDetectorTest::run( int /*start_from */)
     {
         case CHESSBOARD_SB:
             checkByGeneratorHighAccuracy();      // not supported by CHESSBOARD
+            /* fallthrough */
         case CHESSBOARD:
             checkByGenerator();
             if (ts->get_err_code() != cvtest::TS::OK)