patch 9.0.1603: display wrong if scrolling multiple lines with 'smoothscroll'

Problem:    Display wrong when scrolling multiple lines with 'smoothscroll'
            set.
Solution:   Redraw when w_skipcol changed. (closes #12477, closes #12468)
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index 7a95e6f..3806486 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -777,7 +777,7 @@
       call setline(14, 'bbbb')
   END
   call writefile(lines, 'XSmoothIncsearch', 'D')
-  let buf = RunVimInTerminal('-S XSmoothIncsearch', #{rows: 8, cols:40})
+  let buf = RunVimInTerminal('-S XSmoothIncsearch', #{rows: 8, cols: 40})
 
   call term_sendkeys(buf, "/b")
   call VerifyScreenDump(buf, 'Test_smooth_incsearch_1', {})
@@ -792,4 +792,26 @@
   call StopVimInTerminal(buf)
 endfunc
 
+" Test scrolling multiple lines and stopping at non-zero skipcol.
+func Test_smoothscroll_multi_skipcol()
+  CheckScreendump
+
+  let lines =<< trim END
+      setlocal cursorline scrolloff=0 smoothscroll
+      call setline(1, repeat([''], 9))
+      call setline(3, repeat('a', 50))
+      call setline(8, 'bbb')
+      call setline(9, 'ccc')
+      redraw
+  END
+  call writefile(lines, 'XSmoothMultiSkipcol', 'D')
+  let buf = RunVimInTerminal('-S XSmoothMultiSkipcol', #{rows: 10, cols: 40})
+  call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_1', {})
+
+  call term_sendkeys(buf, "3\<C-E>")
+  call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_2', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab