patch 9.0.1000: with 'smoothscroll' skipcol may be reset unnecessarily

Problem:    With 'smoothscroll' skipcol may be reset unnecessarily.
Solution:   Check the line does actually fit in the window.
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index 6f8693b..58a8bf4 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -481,6 +481,13 @@
   exe "normal 20h"
   call s:check_col_calc(1, 4, 61)
 
+  " cursor on last line, "gk" should not cause a scroll
+  set scrolloff=0
+  normal G0
+  call s:check_col_calc(1, 7, 1)
+  normal gk
+  call s:check_col_calc(1, 6, 101)
+
   bwipe!
 endfunc