Having multiple appendix nodes in item node causes panic.

[PokeyTheCat]

I only used the default options in Karabiner. I'm attempting to copy them into a private.xml and convert them to the JSON format. In my first attempt I've made it angry.

$ ./karaconv -i test.private.xml -o test.json
thread 'main' panicked at 'called Result::unwrap() on an Err value: duplicate field appendix', libcore/result.rs:945:5
note: Run with RUST_BACKTRACE=1 for a backtrace.

Example Item node copied from checkbox/for_pc_users.xml that causes issue:

<item>
  <name>Use PC Style Reload</name>
  <appendix>(Control+R to Command_L+R)</appendix>
  <appendix></appendix>
  <appendix>{{ PC_STYLE_BINDINGS_IGNORE_APPS_DESCRIPTION }}</appendix>
  <identifier>remap.copy_paste_winstyle_reload</identifier>
  <not>{{ PC_STYLE_BINDINGS_IGNORE_APPS }}</not>
  {{ PC_STYLE_BINDINGS_IGNORE_EXTRA }}
  <autogen>__KeyToKey__ KeyCode::R, MODIFIERFLAG_EITHER_LEFT_OR_RIGHT_CONTROL, KeyCode::R, ModifierFlag::COMMAND_L</autogen>
</item>