Only reset '0 mark when it is the last window

We only need to reset '0 mark when our tagbar window is the last one,
otherwise, just quit the window and let the other window handle the
error that might happen on quiting Vim.

autoload/tagbar.vim

@@ -3364,7 +3364,11 @@ function! s:QuitIfOnlyWindow() abort
         if tabpagenr('$') == 1
             " Before quitting Vim, delete the tagbar buffer so that
             " the '0 mark is correctly set to the previous buffer.
-            bdelete
+            " Also disable autocmd on this command to avoid unnecessary
+            " autocmd nesting.
+            if winnr('$') == 1
+                noautocmd bdelete
+            endif
             quit
         else
             close