patch 8.0.1151: "vim -c startinsert!" doesn't append

Problem:    "vim -c startinsert!" doesn't append.
Solution:   Correct line number on startup. (Christian Brabandt, closes #2117)
diff --git a/src/testdir/test_startup.vim b/src/testdir/test_startup.vim
index af2b3c1..6f67bfc 100644
--- a/src/testdir/test_startup.vim
+++ b/src/testdir/test_startup.vim
@@ -263,3 +263,27 @@
   call assert_match("defaulting to 'ansi'", out)
   let $TERM = save_term
 endfunc
+
+func Test_zzz_startinsert()
+  " Test :startinsert
+  call writefile(['123456'], 'Xtestout')
+  let after = [
+	\ ':startinsert',
+  \ 'call feedkeys("foobar\<c-o>:wq\<cr>","t")'
+	\ ]
+  if RunVim([], after, 'Xtestout')
+    let lines = readfile('Xtestout')
+    call assert_equal(['foobar123456'], lines)
+  endif
+  " Test :startinsert!
+  call writefile(['123456'], 'Xtestout')
+  let after = [
+	\ ':startinsert!',
+  \ 'call feedkeys("foobar\<c-o>:wq\<cr>","t")'
+	\ ]
+  if RunVim([], after, 'Xtestout')
+    let lines = readfile('Xtestout')
+    call assert_equal(['123456foobar'], lines)
+  endif
+  call delete('Xtestout')
+endfunc