fixed 1 packet off for out of sequence clean up

libi2pd/SSU2Session.cpp

@@ -2132,6 +2132,7 @@ namespace transport
 			if (packet > m_ReceivePacketNum + 1)
 			{
 				// like we've just received all packets before first
+				packet--;
 				m_ReceivePacketNum = packet - 1;
 				UpdateReceivePacketNum (packet);
 			}