patch 8.2.2152: screenpos() does not include the WinBar offset

Problem:    screenpos() does not include the WinBar offset.
Solution:   Use W_WINROW() instead of directly using w_window. (closes #7487)
diff --git a/src/testdir/test_cursor_func.vim b/src/testdir/test_cursor_func.vim
index bfb908d..d914067 100644
--- a/src/testdir/test_cursor_func.vim
+++ b/src/testdir/test_cursor_func.vim
@@ -101,6 +101,11 @@
   close
   call assert_equal({}, screenpos(999, 1, 1))
   bwipe!
+
+  call assert_equal({'col': 1, 'row': 1, 'endcol': 1, 'curscol': 1}, screenpos(win_getid(), 1, 1))
+  nmenu WinBar.TEST :
+  call assert_equal({'col': 1, 'row': 2, 'endcol': 1, 'curscol': 1}, screenpos(win_getid(), 1, 1))
+  nunmenu WinBar.TEST
 endfunc
 
 func Test_screenpos_number()