ytdl seems conflicted if `requestOptions.headers` has `range` on it.

Hi. I have a project called [ytmous](https://github.com/ytmous/ytmous/tree/nightly), and wanting to put my own `range` header with `ytdl.downloadFromInfo(..., { requestOptions: { headers: { range: "...." } } })` so my project could let my clients to seek a video.

But the problem is, This code here seems only checking to `options.range.start`:

https://github.com/fent/node-ytdl-core/blob/99e6c678eb8cf8f330479539ad08ab6a0d444322/lib/index.js#L137-L138

So i wonder if there's any way to solve this problem? Because even i use `options.range.start`:

https://github.com/ytmous/ytmous/blob/nightly/index.js#L191-L193

It's still did not let me to seek any way. Even it does put `{ start: 1234567 }`, Firefox is yelling that the video format is corrupted.