build command throws IndexError
An attempt to run a command
```
p8tool build --lua ./src/main.lua --gfx ./carts/assets.p8 ./carts/out.p8
```
throws a following Error
```
Traceback (most recent call last):
  File "/Users/jakubgruszecki/Documents/picotool/p8tool", line 8, in <module>
    sys.exit(tool.main(sys.argv[1:]))
  File "/Users/jakubgruszecki/Documents/picotool/pico8/tool.py", line 596, in main
    return args.func(args)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/build/build.py", line 258, in do_build
    lua_path=getattr(args, 'lua_path', None))
  File "/Users/jakubgruszecki/Documents/picotool/pico8/build/build.py", line 158, in _evaluate_require
    _evaluate_require(reqd_lua, reqd_filepath, package_lua, lua_path=lua_path)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/build/build.py", line 158, in _evaluate_require
    _evaluate_require(reqd_lua, reqd_filepath, package_lua, lua_path=lua_path)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/build/build.py", line 155, in _evaluate_require
    reqd_lua.reparse(writer_cls=lua.LuaASTEchoWriter)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 178, in reparse
    version=self.version)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 132, in from_lines
    result.update_from_lines(lines)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 141, in update_from_lines
    self._lexer.process_lines(lines)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lexer.py", line 479, in process_lines
    for line in lines:
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 159, in to_lines
    for line in writer.to_lines():
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 943, in to_lines
    for chunk in self.walk():
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 247, in walk
    for t in self._walk(self._root):
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 930, in _walk
    for t in super()._walk(node):
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 228, in _walk
    for t in result:
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 535, in _walk_Chunk
    yield self._get_semis(node)
  File "/Users/jakubgruszecki/Documents/picotool/pico8/lua/lua.py", line 522, in _get_semis
    if self._tokens[self._pos].matches(lexer.TokSymbol(b';')):
IndexError: list index out of range
```
My project on which picotool crashes is in this repo:
https://github.com/ditrytus/coffee-central