Crash when creating Richtext with string where macro appears at the end

[ヽ(*≧ω≦)ﾉ shru]

This code:

local txt

function love.load()
  local Richtext = require 'richtext'
  txt = Richtext:new({
    "Test {somemacro}",
    somemacro = {1, 0, 1},
  })
end

function love.draw()
  txt:draw(10, 10)
end

Will produce the following error:

Error: richtext.lua:85: attempt to index local 'textfragment' (a nil value)
stack traceback:
  [string "boot.lua"]:637: in function '__index'
  richtext.lua:85: in function 'parsefragment'
  richtext.lua:103: in function 'parse'
  richtext.lua:40: in function 'new'
  main.lua:5: in function 'load'
  [string "boot.lua"]:488: in function <[string "boot.lua"]:487>
  [C]: in function 'xpcall'
  [string "boot.lua"]:650: in function <[string "boot.lua"]:639>
  [C]: in function 'xpcall'

I've fixed this by changing the line parsefragment(self.parsedtext, text:match('[^}]+$')) to parsefragment(self.parsedtext, text:match('[^}]+$') or ''), but I'll play around with it for a bit longer before submitting a PR.