Do not try to decode video when EOF is reached

When the video stream socket is closed and read_packey() returns -1,
av_read_frame() still returns 0.

To detect EOF, check the flag eof_reached in the AVIOContext.

This avoids garbage errors on closing.

app/src/decoder.c

@@ -92,7 +92,7 @@ static int run_decoder(void *data) {
     packet.data = NULL;
     packet.size = 0;
 
-    while (!av_read_frame(format_ctx, &packet)) {
+    while (!av_read_frame(format_ctx, &packet) && !avio_ctx->eof_reached) {
 // the new decoding/encoding API has been introduced by:
 // <http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=7fc329e2dd6226dfecaa4a1d7adf353bf2773726>
 #if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(57, 37, 0)