patch 8.0.0394: tabs are not aligned when scrolling horizontally

Problem:    Tabs are not aligned when scrolling horizontally and a Tab doesn't
            fit. (Axel Bender)
Solution:   Handle a Tab as a not fitting character. (Christian Brabandt)
            Also fix that ":redraw" does not scroll horizontally to show the
            cursor.  And fix the test that depended on the old behavior.
diff --git a/src/testdir/test_listlbr.vim b/src/testdir/test_listlbr.vim
index 71366a1..7856ee8 100644
--- a/src/testdir/test_listlbr.vim
+++ b/src/testdir/test_listlbr.vim
@@ -217,3 +217,19 @@
   call s:compare_lines(expect, lines)
   call s:close_windows()
 endfunc
+
+func Test_list_with_tab_and_skipping_first_chars()
+  call s:test_windows('setl list listchars=tab:>- ts=70 nowrap')
+  call setline(1, ["iiiiiiiiiiiiiiii\taaaaaaaaaaaaaaaaaa", "iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii\taaaaaaaaaaaaaaaaaa", "iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii\taaaaaaaaaaaaaaaaaa", "iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii\taaaaaaaaaaaaaaaaaa"])
+  call cursor(4,64)
+  norm! 2zl
+  let lines = s:screen_lines([1, 4], winwidth(0))
+  let expect = [
+\ "---------------aaaaa",
+\ "---------------aaaaa",
+\ "---------------aaaaa",
+\ "iiiiiiiii>-----aaaaa",
+\ ]
+  call s:compare_lines(expect, lines)
+  call s:close_windows()
+endfu