Fixes azure blob binary caching by not sending put headers for get requests and by sending headers only once

[autoantwort]

Fixes #558 (comment)

There were actually two issues:

1. Headers are send twice
2. azure blob headers meant for put requests are also send in get requests (I didn't know that and thought it would be ok to also send them in get requests)

[BillyONeal]

Headers are send twice

Technically headers were sent however many times as you had downloads. O(N^2) headers! :D

[Osyotr]

Thank you very much for a quick fix!