patch 8.2.4204: screenpos() has non-zero row for invisible text

Problem:    screenpos() has non-zero row for invisible text.
Solution:   Only add the window row when the text is visible. (closes #9618)
diff --git a/src/testdir/test_cursor_func.vim b/src/testdir/test_cursor_func.vim
index 965c704..bc12511 100644
--- a/src/testdir/test_cursor_func.vim
+++ b/src/testdir/test_cursor_func.vim
@@ -124,7 +124,7 @@
 	\ 'col': wincol + 7,
 	\ 'curscol': wincol + 7,
 	\ 'endcol': wincol + 7}, winid->screenpos(line('$'), 8))
-  call assert_equal({'row': winrow - 1, 'col': 0, 'curscol': 0, 'endcol': 0},
+  call assert_equal({'row': 0, 'col': 0, 'curscol': 0, 'endcol': 0},
         \ winid->screenpos(line('$'), 22))
 
   close