libhb: fix potential seg fault in hb_hexdump


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6246 b64f7644-9d1e-0410-96f1-a4d463321fa5
libhb: add i-frame detection for mpeg4 ts/ps streams


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6247 b64f7644-9d1e-0410-96f1-a4d463321fa5
fix comment in isIframe()


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6248 b64f7644-9d1e-0410-96f1-a4d463321fa5