LOLWUT: fix crash when col < 2.
LOLWUT: fix crash when col < 2.

Close #5345.

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