fix(terminal): crash when TermClose deletes other buffers

Problem:  Crash when deleting terminal buffer and TermClose deletes
          other buffers.
Solution: Close the terminal after restoring b_nwindows.
(cherry picked from commit 7297e9d339)

src/nvim/buffer.c

@@ -636,10 +636,6 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
     return true;
   }
 
-  if (buf->terminal) {
-    buf_close_terminal(buf);
-  }
-
   // Always remove the buffer when there is no file name.
   if (buf->b_ffname == NULL) {
     del_buf = true;
@@ -663,6 +659,15 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
 
   buf->b_nwindows = nwindows;
 
+  if (buf->terminal) {
+    buf_close_terminal(buf);
+    // Must check this before calling buf_freeall(), otherwise is_curbuf will be true
+    // in buf_freeall() but still false here, leading to a 0-line buffer.
+    if (buf == curbuf && !is_curbuf) {
+      return false;
+    }
+  }
+
   buf_freeall(buf, ((del_buf ? BFA_DEL : 0)
                     + (wipe_buf ? BFA_WIPE : 0)
                     + (ignore_abort ? BFA_IGNORE_ABORT : 0)));

test/functional/autocmd/termxx_spec.lua

@@ -45,6 +45,18 @@ describe('autocmd TermClose', function()
     test_termclose_delete_own_buf()
   end)
 
+  it('TermClose deleting all other buffers', function()
+    local oldbuf = api.nvim_get_current_buf()
+    -- The terminal process needs to keep running so that TermClose isn't triggered immediately.
+    api.nvim_set_option_value('shell', string.format('"%s" INTERACT', testprg('shell-test')), {})
+    command(('autocmd TermClose * bdelete! %d'):format(oldbuf))
+    command('horizontal terminal')
+    neq(oldbuf, api.nvim_get_current_buf())
+    command('bdelete!')
+    feed('<C-G>') -- This shouldn't crash due to having a 0-line buffer.
+    assert_alive()
+  end)
+
   it('triggers when fast-exiting terminal job stops', function()
     command('autocmd TermClose * let g:test_termclose = 23')
     command('terminal')