Gracefully fail, instead of a logic error when a custom parser encounters keys that are not in order

[planetis-m]

proc initFromJson*[T](dst: var Matrix[T]; p: var JsonParser) =
  eat(p, tkCurlyLe)
  var count = 0
  while p.tok != tkCurlyRi:
    if p.tok != tkString:
      raiseParseErr(p, "string literal as key")
    case p.a
    of "m":
      discard getTok(p)
      eat(p, tkColon)
      if count > 1:
        raiseParseErr(p, "JSON keys in order")
      count = 1
      initFromJson(dst.m, p)
    of "n":
      discard getTok(p)
      eat(p, tkColon)
      if count > 2:
        raiseParseErr(p, "JSON keys in order")
      count = 2
      initFromJson(dst.n, p)
    of "data":
      discard getTok(p)
      eat(p, tkColon)
      if count > 3:
        raiseParseErr(p, "JSON keys in order")
      count = 3
      eat(p, tkBracketLe)
      assert dst.m != 0 and dst.n == 0
      dst.data = createData[T](dst.m * dst.n)
      var i = 0
      while p.tok != tkBracketRi:
        initFromJson(dst.data[i], p)
        inc(i)
        if p.tok != tkComma: break
        discard getTok(p)
      eat(p, tkBracketRi)
    else:
      raiseParseErr(p, "valid object field")
    if p.tok != tkComma: break
    discard getTok(p)
  eat(p, tkCurlyRi)

doesn't even seem enough...