putio: fix multithread download and other ranged requests

Before this change the 206 responses from putio Range requests were being
returned as errors.

This change checks for 200 and 206 in the GET response now.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f