http: protocol for output ignores HTTP errors

[maximrazin]

Summary of the bug:

When ffmpeg output uses http: protocol, and HTTP server returns an error (e.g. 404 or 405), the error is ignored completely, it isn't even reflected in logs.

How to reproduce:

Set up a local web server, don't enable HTTP PUT/POST. I used nginx with a default configuration

% ffmpeg -i file.ts -c copy -f mpegts http://localhost/blackhole.ts

HTTP server returns 405, but ffmpeg does not react and completes successfully

Expected behavior:

ffmpeg should log the HTTP error and fail with I/O error

[maximrazin]

Proposed patch