sol: return error if av_get_packet() fails.

This prevents sending a packet with data=NULL size=AVERROR_EOF.
(cherry picked from commit b15a9888a8)

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/sol.c

@@ -132,6 +132,8 @@ static int sol_read_packet(AVFormatContext *s,
     if (s->pb->eof_reached)
         return AVERROR(EIO);
     ret= av_get_packet(s->pb, pkt, MAX_SIZE);
+    if (ret < 0)
+        return ret;
     pkt->stream_index = 0;
 
     /* note: we need to modify the packet size here to handle the last