fix: env issue importing remote video source

[luwes]

this was throwing with a remote video import

next-video/src/assets.ts

Lines 74 to 75 in 253015f

	const VIDEOS_DIR = JSON.parse(env['__NEXT_VIDEO_OPTS'] ?? '{}').folder;
	if (!VIDEOS_DIR) throw new Error('Missing video `folder` config.');

[luwes]

I noticed the build fail, this worked locally so must be solvable..