ffmpeg: Fix crash when avio_check is called
ffmpeg: Fix crash when avio_check is called

url_check does not guarantee url_open will be called before
(and actually it is not designed to do so)
If url_open is not called before url_check called, ffs
will be null causing the crash.

Change-Id: I0176c619eeb931ede0061003e396ee7e1407b860
(cherry picked from commit 832d93744cccf1f056f7ecdad6041e91148e9260)

TeamExodus/external_stagefright-plugins,TeamExodus/external_stagefright-plugins