avformat/sctp: add size check in sctp_read() matching sctp_write()

Commit 5b98cea4 added a size < 2 guard to sctp_write() to prevent
out-of-bounds access when max_streams is enabled, but the identical
pattern in sctp_read() was not addressed.

When max_streams is non-zero, sctp_read() passes (buf + 2, size - 2)
to ff_sctp_recvmsg(). If size < 2, size - 2 wraps to a large value
on the implicit cast to size_t in the callee.

Add the same guard.

Signed-off-by: bird <6666242+bird@users.noreply.github.com>

libavformat/sctp.c

@@ -309,6 +309,9 @@ static int sctp_read(URLContext *h, uint8_t *buf, int size)
     }
 
     if (s->max_streams) {
+        if (size < 2)
+            return AVERROR(EINVAL);
+
         /*StreamId is introduced as a 2byte code into the stream*/
         struct sctp_sndrcvinfo info = { 0 };
         ret = ff_sctp_recvmsg(s->fd, buf + 2, size - 2, NULL, 0, &info, 0);