Streams: fix xreadgroup crash after xgroup SETID is sent.
Streams: fix xreadgroup crash after xgroup SETID is sent.

For issue #5111.

soveran/redis,oranagra/redis,soveran/redis,charsyam/redis,oranagra/redis,neomantra/redis,GitHubMota/redis,ofirluzon/redis,nnog/redis,charsyam/redis,GitHubMota/redis,spinlock/redis,pmem/redis,ofirluzon/redis,antirez/redis,PKRoma/redis,soloestoy/redis,charsyam/redis,ctripcorp/redis,PKRoma/redis,oranagra/redis,pmem/redis,spinlock/redis,yossigo/redis,ofirluzon/redis,yossigo/redis,yossigo/redis,PKRoma/redis,soloestoy/redis,GitHubMota/redis,yossigo/redis,neomantra/redis,oranagra/redis,yossigo/redis,antirez/redis,PKRoma/redis,antirez/redis,ofirluzon/redis,GitHubMota/redis,soloestoy/redis,pmem/redis,ctripcorp/redis,neomantra/redis,ctripcorp/redis,spinlock/redis,antirez/redis,oranagra/redis,charsyam/redis,charsyam/redis,nnog/redis,ctripcorp/redis,neomantra/redis,nnog/redis,soloestoy/redis,soloestoy/redis,nnog/redis,pmem/redis,soveran/redis,spinlock/redis,neomantra/redis,PKRoma/redis,soveran/redis,ofirluzon/redis