patch 9.0.0646: with 'smoothscroll' CTRL-E is wrong when 'foldmethod' set

Problem:    with 'smoothscroll' set CTRL-E does not work properly when
            'foldmethod' is set to "indent". (Yee Cheng Chin)
Solution:   Merge the code for scroling with folds and 'smoothscroll'.
            (closes #11262)
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index 876ccf2..e23068f 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -88,6 +88,21 @@
   call term_sendkeys(buf, "\<C-Y>")
   call VerifyScreenDump(buf, 'Test_smoothscroll_8', {})
 
+  if has('folding')
+    call term_sendkeys(buf, ":set foldmethod=indent\<CR>")
+    " move the cursor so we can reuse the same dumps
+    call term_sendkeys(buf, "5G")
+    call term_sendkeys(buf, "\<C-E>")
+    call VerifyScreenDump(buf, 'Test_smoothscroll_1', {})
+    call term_sendkeys(buf, "\<C-E>")
+    call VerifyScreenDump(buf, 'Test_smoothscroll_2', {})
+    call term_sendkeys(buf, "7G")
+    call term_sendkeys(buf, "\<C-Y>")
+    call VerifyScreenDump(buf, 'Test_smoothscroll_7', {})
+    call term_sendkeys(buf, "\<C-Y>")
+    call VerifyScreenDump(buf, 'Test_smoothscroll_8', {})
+  endif
+
   call StopVimInTerminal(buf)
 endfunc