rtpdec: Handle more received packets than expected when sending RR

Without this, we'd signal a huge loss rate (due to unsigned
wraparound) if we had received one packet more than expected (that
is, one seq number sent twice). The code has a check for lost_interval
<= 0, but that doesn't do what was intended as long as the variable is
unsigned.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtpdec.c

@@ -258,7 +258,7 @@ int ff_rtp_check_and_send_back_rr(RTPDemuxContext *s, URLContext *fd,
     uint32_t extended_max;
     uint32_t expected_interval;
     uint32_t received_interval;
-    uint32_t lost_interval;
+    int32_t  lost_interval;
     uint32_t expected;
     uint32_t fraction;