vim-patch:8.2.4217: illegal memory access when undo makes Visual area invalid

Problem:    Illegal memory access when undo makes Visual area invalid.
Solution:   Correct the Visual area after undo.
8d02ce1ed7

vim-patch:8.2.4218: illegal memory access with bracketed paste in Ex mode (N/A)

src/nvim/testdir/test_visual.vim

@@ -1162,5 +1162,20 @@ func Test_visual_ex_copy_line()
   bwipe!
 endfunc
 
+" This was leaving the end of the Visual area beyond the end of a line.
+" Set 'undolevels' to start a new undo block.
+func Test_visual_undo_deletes_last_line()
+  new
+  call setline(1, ["aaa", "ccc", "dyd"])
+  set undolevels=100
+  exe "normal obbbbbbbbbxbb\<Esc>"
+  set undolevels=100
+  /y
+  exe "normal ggvjfxO"
+  undo
+  normal gNU
+  bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/nvim/undo.c

@@ -2633,6 +2633,10 @@ static void u_undo_end(bool did_undo, bool absolute, bool quiet)
     }
   }
 
+  if (VIsual_active) {
+    check_pos(curbuf, &VIsual);
+  }
+
   smsg_attr_keep(0,
                  _("%" PRId64 " %s; %s #%" PRId64 "  %s"),
                  u_oldcount < 0 ? (int64_t)-u_oldcount : (int64_t)u_oldcount,