gst-ffmpeg: error_concealment: Check that the picture is not in a half

Fixes state becoming inconsistent
Fixes a null pointer dereference

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 23318a57358358e7a4dc551e830e4503f0638cfe)

Upstream-Status: Backport 

Signed-off-by: Yue Tao <yue.tao@windriver.com>

---
 libavcodec/error_resilience.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/libavcodec/error_resilience.c b/libavcodec/error_resilience.c
index 01f7424..2b6bc42 100644
--- a/gst-libs/ext/libav/libavcodec/error_resilience.c
+++ b/gst-libs/ext/libav/libavcodec/error_resilience.c
@@ -793,6 +793,12 @@ void ff_er_frame_end(MpegEncContext *s){
        s->picture_structure != PICT_FRAME || // we dont support ER of field pictures yet, though it should not crash if enabled
        s->error_count==3*s->mb_width*(s->avctx->skip_top + s->avctx->skip_bottom)) return;
 
+    if (   s->picture_structure == PICT_FRAME
+        && s->current_picture.linesize[0] != s->current_picture_ptr->linesize[0]) {
+        av_log(s->avctx, AV_LOG_ERROR, "Error concealment not possible, frame not fully initialized\n");
+        return;
+    }
+
     if(s->current_picture.motion_val[0] == NULL){
         av_log(s->avctx, AV_LOG_ERROR, "Warning MVs not available\n");
 
-- 
1.7.5.4