patch 9.0.1072: screenpos() column result in fold may be too small

Problem:    screenpos() column result in fold may be too small.
Solution:   Add space of 'number', sign column, etc. (closes #11715)
diff --git a/src/testdir/test_cursor_func.vim b/src/testdir/test_cursor_func.vim
index fe64be0..d74255e 100644
--- a/src/testdir/test_cursor_func.vim
+++ b/src/testdir/test_cursor_func.vim
@@ -150,8 +150,12 @@
   redraw
   call assert_equal(2, screenpos(1, 2, 1).row)
   call assert_equal(#{col: 1, row: 3, endcol: 1, curscol: 1}, screenpos(1, 3, 1))
-  call assert_equal(3, screenpos(1, 4, 1).row)
-  call assert_equal(3, screenpos(1, 5, 1).row)
+  call assert_equal(#{col: 1, row: 3, endcol: 1, curscol: 1}, screenpos(1, 4, 1))
+  call assert_equal(#{col: 1, row: 3, endcol: 1, curscol: 1}, screenpos(1, 5, 1))
+  setlocal number
+  call assert_equal(#{col: 5, row: 3, endcol: 5, curscol: 5}, screenpos(1, 3, 1))
+  call assert_equal(#{col: 5, row: 3, endcol: 5, curscol: 5}, screenpos(1, 4, 1))
+  call assert_equal(#{col: 5, row: 3, endcol: 5, curscol: 5}, screenpos(1, 5, 1))
   call assert_equal(4, screenpos(1, 6, 1).row)
   bwipe!
 endfunc