dxa: fix decoding of first I-frame by separating I/P-frame decoding

5ef7c84 broke decoding for the first keyframe due to an unnecessary
check for a reference frame.

CC: libav-stable@libav.org

libavcodec/dxa.c

@@ -252,22 +252,27 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame, AVPac
         }
         break;
     case 2:
-    case 3:
     case 4:
+        frame->key_frame = 1;
+        frame->pict_type = AV_PICTURE_TYPE_I;
+        for (j = 0; j < avctx->height; j++) {
+                memcpy(outptr, srcptr, avctx->width);
+            outptr += stride;
+            srcptr += avctx->width;
+        }
+        break;
+    case 3:
     case 5:
         if (!tmpptr) {
             av_log(avctx, AV_LOG_ERROR, "Missing reference frame.\n");
             return AVERROR_INVALIDDATA;
         }
-        frame->key_frame = !(compr & 1);
-        frame->pict_type = (compr & 1) ? AV_PICTURE_TYPE_P : AV_PICTURE_TYPE_I;
-        for(j = 0; j < avctx->height; j++){
-            if(compr & 1){
-                for(i = 0; i < avctx->width; i++)
-                    outptr[i] = srcptr[i] ^ tmpptr[i];
-                tmpptr += stride;
-            }else
-                memcpy(outptr, srcptr, avctx->width);
+        frame->key_frame = 0;
+        frame->pict_type = AV_PICTURE_TYPE_P;
+        for (j = 0; j < avctx->height; j++) {
+            for (i = 0; i < avctx->width; i++)
+                outptr[i] = srcptr[i] ^ tmpptr[i];
+            tmpptr += stride;
             outptr += stride;
             srcptr += avctx->width;
         }