vim-patch:8.0.0331

Problem:    Restoring help snapshot accesses freed memory. (Dominique Pelle)
Solution:   Don't restore a snapshot when the window closes.

343b8c0429

src/nvim/testdir/test_help.vim

@@ -0,0 +1,16 @@
+
+" Tests for :help
+
+func Test_help_restore_snapshot()
+  help
+  set buftype=
+  help
+  edit x
+  help
+  helpclose
+endfunc
+
+func Test_help_errors()
+  call assert_fails('help doesnotexist', 'E149:')
+  call assert_fails('help!', 'E478:')
+endfunc

src/nvim/window.c

@@ -5365,10 +5365,8 @@ restore_snapshot (
   clear_snapshot(curtab, idx);
 }
 
-/*
- * Check if frames "sn" and "fr" have the same layout, same following frames
- * and same children.
- */
+/// Check if frames "sn" and "fr" have the same layout, same following frames
+/// and same children.  And the window pointer is valid.
 static int check_snapshot_rec(frame_T *sn, frame_T *fr)
 {
   if (sn->fr_layout != fr->fr_layout