comctl32/tests: make sure to use a return value (LLVM/Clang) (5/6)

[Austin English]

-- 
-Austin
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diff --git a/dlls/comctl32/tests/trackbar.c b/dlls/comctl32/tests/trackbar.c
index ac67d50..8eaedf4 100644
--- a/dlls/comctl32/tests/trackbar.c
+++ b/dlls/comctl32/tests/trackbar.c
@@ -527,6 +527,7 @@ static void test_line_size(HWND hWndTrackbar){
 
     /* test TBM_SETLINESIZE */
     r = SendMessage(hWndTrackbar, TBM_SETLINESIZE, 0, 10);
+    expect(1,r);
     r = SendMessage(hWndTrackbar, TBM_SETLINESIZE, 0, 4);
     expect(10, r);