os: Always create lock file on explicit display
I.e., even if "-displayfd" is also specified. This is because, in this case, the server creation process is essentially the same as when "-displayfd" is not specified. The only difference with the latter case should be that Xorg outputs the passed display to the display FD (only the display selection logic is bypassed). Signed-off-by: Olivier Certner <olce.freedesktop@certner.fr>