avformat/electronicarts: Clear partial_packet on error

Fixes: Infinite loop
Fixes: 30165/clusterfuzz-testcase-minimized-ffmpeg_dem_EA_fuzzer-6224642371092480

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

libavformat/electronicarts.c

@@ -728,6 +728,7 @@ get_video_packet:
                 ret = av_get_packet(pb, pkt, chunk_size);
             if (ret < 0) {
                 packet_read = 1;
+                partial_packet = 0;
                 break;
             }
             partial_packet = chunk_type == MVIh_TAG;