Revert "Reduce buffer size used while scanning media."

This reverts commit 3345a03162f704d70081fe558d4ce6e7659bf323.
Rewrite of StreamingRingBuffer::safe_read

safe_read was based on FFmpeg's ffurl_read_complete, however when an EOF or an error is encountered, ffurl_read_complete returns the error code rather than the number of bytes read so far.
Rather than wait for FFmpeg to fix it (ref: https://ffmpeg.org/trac/ffmpeg/ticket/2537) ; work around it.
safe_read now will set errno as expected and always return a value >= 0 representing the number of bytes actually read.

Fixes #11263