Avcodec: Fix potential dereference before null check

See CID #1223114
avcodec: map 8088flex TMV

Sample:
http://samples.mplayerhq.hu/fate-suite/tmv/pop-partial.tmv

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Wing Commander III video

Sample:
http://samples.mplayerhq.hu/fate-suite/wc3movie/SC_32-part.MVE

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Westwood VQA

Sample:
http://samples.mplayerhq.hu/fate-suite/vqa/cc-demo1-partial.vqa

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map American Laser Games MM Video

Sample:
http://fate-suite.libav.org/alg-mm/ibmlogo.mm

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Creature Shock AVS

Sample:
http://fate-suite.libav.org/creatureshock-avs/OUTATIME.AVS

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Delphine CIN video

Sample:
http://fate-suite.libav.org/delphine-cin/LOGO-partial.CIN

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Tiertex SEQ video

Sample:
http://fate-suite.libav.org/tiertex-seq/Gameover.seq

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Feeble Files/ScummVM DXA

Sample:
http://fate-suite.libav.org/dxa/meetsquid.dxa

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Interplay C93

Sample:
http://fate-suite.libav.org/cyberia-c93/intro1.c93

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Bethesda VID

Sample:
http://fate-suite.libav.org/bethsoft-vid/ANIM0001.VID

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Beam Software VB

Sample:
http://fate-suite.libav.org/SIFF/INTRO_B.VB

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map RL2 video

Sample:
http://samples.mplayerhq.hu/game-formats/voyeur-rl2/A1100100.RL2

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map BFI video

Sample:
http://fate-suite.libav.org/bfi/2287.bfi

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Electronic Arts CMV

Sample:
http://fate-suite.libav.org/ea-cmv/TITLE.CMVhttp://fate-suite.libav.org/ea-cmv/TITLE.CMV

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map Motion Pixels

Sample:
http://fate-suite.libav.org/motion-pixels/INTRO-partial.MVI

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map EA TGV and SEAD

Sample:
http://fate-suite.libav.org/ea-tgv/INTEL_S.TGV

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map EA TGQ

Sample:
http://fate-suite.libav.org/ea-tgq/v27.tgq

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map EA MAD and EA ADPCM R1

Sample:
http://fate-suite.libav.org/ea-mad/NFS6LogoE.mad

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
avcodec: map PCM_S16LE_PLANAR

Sample:
http://fate-suite.libav.org/ea-mad/xeasport.mad

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>