Avoid the need to use seeking for getting the file size, use fstat
instead, which is significantly faster.

See thread:
Subject: [FFmpeg-devel] [PATCH] Add support to AVSEEK_SIZE to the file protocol seek callback
Date: Fri, 2 Apr 2010 13:13:27 +0200

Originally committed as revision 22799 to svn://svn.ffmpeg.org/ffmpeg/trunk