Do not initialize SDL video when not necessary

The SDL video subsystem is required for video playback and clipboard
synchronization.

If neither is used, it is not necessary to initialize it.

Refs 5e59ed31352251791679e5931d7e5abf0c2d18f6
Refs 110b3a16f6d02124a4567d2ab79fcb74d78f949f
Refs #4418 <https://github.com/Genymobile/scrcpy/issues/4418>
Refs #4477 <https://github.com/Genymobile/scrcpy/issues/4477>