Subtitles can be compiled in non-chronological order

[autotel]

I don't know if this qualifies as an issue, but in case it is any use for you.

It is possible to compile a vtt with subtitles in non chronological order. In order to produce this:

let webvtt=require("node-webvtt");
console.log(webvtt.compile({
    "valid":true,
    "cues":[
        {
           "identifier":"",
           "start":30,
           "end":31,
           "text":"This is a subtitle",
           "styles":"align:start line:0%"
        },
       {
          "identifier":"",
          "start":0,
          "end":1,
          "text":"Hello world!",
          "styles":""
       },
       {
          "identifier":"",
          "start":60,
          "end":61,
          "text":"Foo",
          "styles":""
       },
       {
          "identifier":"",
          "start":110,
          "end":111,
          "text":"Bar",
          "styles":""
       }
    ]
 }));

Whether this is a bug or not, depends on whether a non-chronological vtt file is admissible.

[osk]

I would categorize that as a bug since the resulting webvtt is invalid. I'll add a check against this and update. Thanks!