Fixes/rewrites on videos.php (#5489)

* Fixes/rewrites:
- use empty()/isset() instead of deprecated x()
- merged 2 nested if() blocks into one
- avoided nested if() block inside else block by rewriting it to elseif()
- $contact_id is an integer, let's test on > 0 here
- added a lot spaces and some empty lines for better readability

* CR request:
- removed stray spaces
- added some where they improve readability