pkg/proc: Fix ThreadId when ErrNoGoroutine on g0 stack in GetG
pkg/proc: Fix ThreadId when ErrNoGoroutine on g0 stack in GetG

Avoid always showing `no G executing on thread 0` when ErrNoGoroutine on
g0 stack in GetG.

aarzilli/delve,go-delve/delve,aarzilli/delve,aarzilli/delve,derekparker/delve,aarzilli/delve,go-delve/delve,derekparker/delve,derekparker/delve,go-delve/delve,go-delve/delve,go-delve/delve