rv34: error out on size changes with frame threading

(cherry picked from commit cb7190cd2c691fd93e4d3664f3fce6c19ee001dd)

Fixes: CVE-2012-2772 (according to Ubuntu)
indeo5dec: Make sure we have had a valid gop header.

This prevents decoding happening on a half initialized context.

Fixes CVE-2012-2779

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit 891918431db628db17885ed947ee387b29826a64)

Conflicts:

	libavcodec/ivi_common.c
	libavcodec/ivi_common.h