patch 8.1.1336: some eval functionality is not covered by tests

Problem:    Some eval functionality is not covered by tests.
Solution:   Add a few more test cases. (Masato Nishihata, closes #4374)
diff --git a/src/testdir/test_bufline.vim b/src/testdir/test_bufline.vim
index d2d6929..9c29a05 100644
--- a/src/testdir/test_bufline.vim
+++ b/src/testdir/test_bufline.vim
@@ -8,7 +8,7 @@
   hide
   call assert_equal(0, setbufline(b, 1, ['foo', 'bar']))
   call assert_equal(['foo'], getbufline(b, 1))
-  call assert_equal(['bar'], getbufline(b, 2))
+  call assert_equal(['bar'], getbufline(b, '$'))
   call assert_equal(['foo', 'bar'], getbufline(b, 1, 2))
   exe "bd!" b
   call assert_equal([], getbufline(b, 1, 2))
@@ -81,6 +81,7 @@
   call setline(1, ['a', 'b', 'c'])
   let b = bufnr('%')
   wincmd w
+  call assert_equal(1, appendbufline(b, -1, ['x']))
   call assert_equal(1, appendbufline(b, 4, ['x']))
   call assert_equal(1, appendbufline(1234, 1, ['x']))
   call assert_equal(0, appendbufline(b, 3, ['d', 'e']))
@@ -130,8 +131,11 @@
   exe "bd!" b
   call assert_equal(1, deletebufline(b, 1))
 
+  call assert_equal(1, deletebufline(-1, 1))
+
   split Xtest
   call setline(1, ['a', 'b', 'c'])
+  call cursor(line('$'), 1)
   let b = bufnr('%')
   wincmd w
   call assert_equal(1, deletebufline(b, 4))