eamad: Check against minimum supported dimensions

Fixes out of array reads

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/eamad.c

@@ -257,6 +257,11 @@ static int decode_frame(AVCodecContext *avctx,
     calc_quant_matrix(s, buf[13]);
     buf += 16;
 
+    if (width < 16 || height < 16) {
+        av_log(avctx, AV_LOG_ERROR, "Dimensions too small\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     if (avctx->width != width || avctx->height != height) {
         if((width * height)/2048*7 > buf_end-buf)
             return AVERROR_INVALIDDATA;