Open WebUI: Redirect-Bypass SSRF in OAuth `_process_picture_url` (incomplete-fix sibling of CVE-2026-45401)

Summary backend/openwebui/utils/oauth.py::processpictureurl v0.9.5, lines 1435-1470 calls validateurlpictureurl on the initial URL only, then invokes aiohttp.ClientSession.getpictureurl, ... without allowredirects=False. aiohttp's default is allowredirects=True, maxredirects=10; the function does...