patch 8.1.0171: typing CTRL-W n in a terminal window causes ml_get error

Problem:    Typing CTRL-W n in a terminal window causes ml_get error.
Solution:   When resizing the terminal outside of terminal_loop() make sure
            the snapshot is complete.

src/terminal.c

@@ -3134,13 +3134,16 @@ term_update_window(win_T *wp)
 
     if (term->tl_rows != newrows || term->tl_cols != newcols)
     {
-
-
 	term->tl_vterm_size_changed = TRUE;
 	vterm_set_size(vterm, newrows, newcols);
 	ch_log(term->tl_job->jv_channel, "Resizing terminal to %d lines",
 								      newrows);
 	term_report_winsize(term, newrows, newcols);
+
+	// Updating the terminal size will cause the snapshot to be cleared.
+	// When not in terminal_loop() we need to restore it.
+	if (term != in_terminal_loop)
+	    may_move_terminal_to_buffer(term, FALSE);
     }
 
     /* The cursor may have been moved when resizing. */

src/testdir/test_terminal.vim

@@ -1525,6 +1525,32 @@ func Test_terminwinscroll()
   exe buf . 'bwipe!'
 endfunc
 
+" Resizing the terminal window caused an ml_get error.
+" TODO: This does not reproduce the original problem.
+func Test_terminal_resize()
+  set statusline=x
+  terminal
+  call assert_equal(2, winnr('$'))
+
+  " Fill the terminal with text.
+  if has('win32')
+    call feedkeys("dir\<CR>", 'xt')
+  else
+    call feedkeys("ls\<CR>", 'xt')
+  endif
+  " Go to Terminal-Normal mode for a moment.
+  call feedkeys("\<C-W>N", 'xt')
+  " Open a new window
+  call feedkeys("i\<C-W>n", 'xt')
+  call assert_equal(3, winnr('$'))
+  redraw
+
+  close
+  call assert_equal(2, winnr('$'))
+  call feedkeys("exit\<CR>", 'xt')
+  set statusline&
+endfunc
+
 " must be nearly the last, we can't go back from GUI to terminal
 func Test_zz1_terminal_in_gui()
   if !CanRunGui()

src/version.c

@@ -789,6 +789,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    171,
 /**/
     170,
 /**/