avcodec/indeo5: Do not leave frame_type set to an invalid value

Fixes: null pointer dereference
Fixes: 5264/clusterfuzz-testcase-minimized-4621956621008896

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/indeo5.c

@@ -324,6 +324,7 @@ static int decode_pic_hdr(IVI45DecContext *ctx, AVCodecContext *avctx)
     ctx->frame_type      = get_bits(&ctx->gb, 3);
     if (ctx->frame_type >= 5) {
         av_log(avctx, AV_LOG_ERROR, "Invalid frame type: %d \n", ctx->frame_type);
+        ctx->frame_type = FRAMETYPE_INTRA;
         return AVERROR_INVALIDDATA;
     }