fix media upload in create_tweet example

[dwrensha]

Fixes #125.

If handle.progress is None, as it commonly is for image uploads, then get_status() will return a 404, so we need to check it before calling get_status().

I tested that this works both with an image upload, where progress is None, and a video upload, where progress is non None.

[OneSecure]

I have tested it. It's work fine. Thanks.

[dwrensha]

What would the reason be for that modification to Cargo.toml? Does cargo build --example create_tweet not work?

[OneSecure]

Sorry I'm newbee in rust.