AVideo Encoder downloadURL SSRF via unpinned retry fallback

AVideo versions from commit 0dbadbca through latest master contain a server-side request forgery vulnerability in the encoder download-by-URL flow due to an unpinned retry fallback that bypasses DNS pinning validation. An authenticated attacker can supply a downloadURL that redirects to an internal address, causing the unpinned retry to follow the redirect and reach internal targets for blind SSRF attacks.