Fix issue where when RTP timestamp does not change and packet loss occurs, the rtp parser's CommonRtpDecoder never outputs again (#3891)

Co-authored-by: TalusL <liangzhuohua@genew.com>

src/Extension/CommonRtp.cpp

@@ -57,6 +57,10 @@ bool CommonRtpDecoder::inputRtp(const RtpPacket::Ptr &rtp, bool){
     }
 
     _last_seq = seq;
+
+    if (_drop_flag && rtp->getHeader()->mark) {
+        _drop_flag = false;
+    }
     return false;
 }