Fix potential race in bugReportStart
Fix potential race in bugReportStart

this race would only happen when two threads paniced at the same time,
and even then the only consequence is some extra log lines.

race reported in #7391

soloestoy/redis,antirez/redis,yossigo/redis,soloestoy/redis,charsyam/redis,neomantra/redis,ctripcorp/redis,oranagra/redis,oranagra/redis,yossigo/redis,PKRoma/redis,antirez/redis,PKRoma/redis,charsyam/redis,PKRoma/redis,antirez/redis,neomantra/redis,soloestoy/redis,ctripcorp/redis,charsyam/redis,neomantra/redis,PKRoma/redis,ctripcorp/redis,oranagra/redis,charsyam/redis,ofirluzon/redis,charsyam/redis,soloestoy/redis,antirez/redis,ofirluzon/redis,yossigo/redis,ofirluzon/redis,yossigo/redis,neomantra/redis,neomantra/redis,PKRoma/redis,yossigo/redis,ctripcorp/redis,ofirluzon/redis,oranagra/redis,oranagra/redis,ofirluzon/redis,soloestoy/redis