adpcm: ADPCM Electronic Arts has always two channels

Fixes half of http://ffmpeg.org/trac/ffmpeg/ticket/794
Adresses CVE-2012-0852

(cherry picked from commit bb5b3940b08d8dad5b7e948e8f3b02cd2eb70716)

Conflicts:

	libavcodec/adpcm.c

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
(cherry picked from commit b581580bd1cc8506befa65b0a5c9ae429240f21f)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
(cherry picked from commit a0f58c3a605b8123039628d1598cb36f1da0e815)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
diff --git a/libavcodec/adpcm.c b/libavcodec/adpcm.c
index 994c0c6..8eff05e 100644
--- a/libavcodec/adpcm.c
+++ b/libavcodec/adpcm.c
@@ -667,17 +667,23 @@
 static av_cold int adpcm_decode_init(AVCodecContext * avctx)
 {
     ADPCMContext *c = avctx->priv_data;
+    unsigned int min_channels = 1;
     unsigned int max_channels = 2;
 
     switch(avctx->codec->id) {
+    case CODEC_ID_ADPCM_EA:
+        min_channels = 2;
+        break;
     case CODEC_ID_ADPCM_EA_R1:
     case CODEC_ID_ADPCM_EA_R2:
     case CODEC_ID_ADPCM_EA_R3:
         max_channels = 6;
         break;
     }
-    if(avctx->channels > max_channels){
-        return -1;
+
+    if (avctx->channels < min_channels || avctx->channels > max_channels) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid number of channels\n");
+        return AVERROR(EINVAL);
     }
 
     switch(avctx->codec->id) {