Fixed a bug that in rare case kcptun will hang

1. Fixed a bug in smux that in rare case, kcptun will hang up forever in smux.stream.OpenStream() & smux.stream.Close()

$ go version
go version go1.20 linux/amd64

$ date
Tue Feb 14 22:27:58 CST 2023

$ ./build-release.sh
Setting GO111MODULE to on
1783047eba56c897a7f32a39fef0b6398593cc16  kcptun-linux-amd64-20230214.tar.gz
ac3b1aef1d5e3fb5cdfe4fcad6a8424ca7a18953  kcptun-darwin-amd64-20230214.tar.gz
b15f165a92b8754f7fc72160fec78ea992c647f5  kcptun-windows-amd64-20230214.tar.gz
7f192c2171c543789f33661dde1144c2b9e66bac  kcptun-freebsd-amd64-20230214.tar.gz
9aaaa19753a165276efdada10191a9c6d4f05d16  kcptun-linux-386-20230214.tar.gz
e169df4c8b9f95131e464a4cd171e8b2878ee2c4  kcptun-windows-386-20230214.tar.gz
b3a5b4cecd033b2921854bb09bf30141d089a6fa  kcptun-linux-arm5-20230214.tar.gz
38aed3cfaf7af2128e3fc623ce2447668c18d908  kcptun-linux-arm6-20230214.tar.gz
40432caa951a85b8094938548db232cb379bfcc9  kcptun-linux-arm7-20230214.tar.gz
270f0bbac8bdaf5475494d40318d1cbe013c552f  kcptun-linux-arm64-20230214.tar.gz
08d2e14702010a68bb0ffd2f769c71772af93336  kcptun-darwin-arm64-20230214.tar.gz
ba204001f743a0e870991a217fb4ffbdcc7db1c5  kcptun-windows-arm64-20230214.tar.gz
3bdaef986c882b262132b5909c1092850c5d604a  kcptun-linux-mipsle-20230214.tar.gz
fa7bfc667e490b2f0bba1c8241253a41d8338b2e  kcptun-linux-mips-20230214.tar.gz