Reverse error checking logic to make sure lock errors are logged

[KevinGreen]

Noticed this potential issue while reading through this code. Due to how the flock library will set always return (false, err) this code wouldn't print other lock errors since it would always hit the first branch. This flips the logic to make sure the err is checked first then falls through when the more typical case of the lock being held by someone else most of the time. gofrs/flock will never return (true, err): https://github.com/gofrs/flock/blob/master/flock_unix.go#L158