Use AVInputFormat.name instead of AVInputFormat.long_name for container formats

Submitted by Sebastian Dröge @slomo

Link to original bug (#738060)

Description

long_name is meant to be human readable and can change, while name is a comma separated list of machine usable container format names. long_name can change or be reformatted any time.

Also long_name can be NULL, especially if building libav/ffmpeg with --enable-small