fix media comments for discussions with tons of videos
fix media comments for discussions with tons of videos

if you called $().mediaCommentThumbnail() with an
empty set it would break it so it won't make mediaCommentThumbails
any more for anything else.

Change-Id: I1a8868439563df7655c07d1aedfada37ad4db857
fixes: #8874
Reviewed-on: https://gerrit.instructure.com/11522
Reviewed-by: Zach Wily <9de8c4480303b5335cd2a33eefe814615ba3612a@instructure.com>
Tested-by: Zach Wily <9de8c4480303b5335cd2a33eefe814615ba3612a@instructure.com>

samuels410/greatlakes-lms,utkarshx/canvas-lms,jay3126/canvas-lms,wye0220/shindig-canvas,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,leftplusrightllc/canvas-lms,shidao-fm/canvas-lms,Jyaasa/canvas-lms,venturehive/canvas-lms,Unow/canvas-lms,va7map/canvas-lms,skmezanul/canvas-lms,fronteerio/canvas-lms,grahamb/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,wrdsb/canvas-lms,arrivu/arrivu-lms,fronteerio/canvas-lms,parbros/red-innovadores-lms,antoniuslin/canvas-lms,greyhwndz/canvas-lms,arrivu/hoodemo,rup/Tarrax,SwinburneOnline/canvas-lms,arrivu/qibla-ecampus,wimemx/Canvas,roxolan/canvas-lms,Jyaasa/canvas-lms,tgroshon/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,sfu/canvas-lms,efrj/canvas-lms,djbender/canvas-lms,whalejasmine/canvas-lms,fronteerio/canvas-lms,arrivu/arrivu-lms,tgroshon/canvas-lms,HotChalk/canvas-lms,shidao-fm/canvas-lms,nditech/red-innovadores-lms,merichar/canvas-lms,va7map/canvas-lms,Rvor/canvas-lms,Unow/ins,arrivu/hoodemo,rup/Tarrax,kyroskoh/canvas-lms,HotChalk/canvas-lms,sli7246/canvas_branch,samuels410/greatlakes-lms,whalejasmine/canvas-lms,venturehive/canvas-lms,kyroskoh/canvas-lms,merichar/canvas-lms,va7map/canvas-lms,leftplusrightllc/canvas-lms,usmschuck/canvas,whalejasmine/canvas-lms,skmezanul/canvas-lms,ankithbti/canvas_lms,tgroshon/canvas-lms,arrivu/qibla-ecampus,HotChalk/canvas-lms,landonwilkins/canvas-lms,juoni/canvas-lms,efrj/canvas-lms,skmezanul/canvas-lms,jay3126/canvas-lms,loganrun/pincan,venturehive/canvas-lms,usmschuck/canvas,redconfetti/canvas-lms,SwinburneOnline/canvas-lms,parbros/red-innovadores-lms,greyhwndz/canvas-lms,roxolan/canvas-lms,Jyaasa/canvas-lms,utkarshx/canvas-lms,Rvor/canvas-lms,ShreniiNepal/shrenii_lmp,redconfetti/canvas-lms,redconfetti/canvas-lms,loganrun/pincan,grahamb/canvas-lms,ShreniiNepal/shrenii_lmp,sli7246/canvas_branch,sfu/canvas-lms,jay3126/canvas-lms,greyhwndz/canvas-lms,utkarshx/canvas-lms,greyhwndz/canvas-lms,ankithbti/canvas_lms,sfu/canvas-lms,sdeleon28/canvas-lms,antoniuslin/canvas-lms,arrivu/jigsaw-lms,sli7246/canvas_branch,djbender/canvas-lms,HotChalk/canvas-lms,Rvor/canvas-lms,grahamb/canvas-lms,SwinburneOnline/canvas-lms,juoni/canvas-lms,usmschuck/canvas,usmschuck/canvas,wimemx/Canvas,skmezanul/canvas-lms,utkarshx/canvas-lms,ShreniiNepal/shrenii_lmp,Unow/ins,tgroshon/canvas-lms,va7map/canvas-lms,rup/Tarrax,sfu/canvas-lms,kyroskoh/canvas-lms,roxolan/canvas-lms,redconfetti/canvas-lms,shidao-fm/canvas-lms,arrivu/jigsaw-lms,Rvor/canvas-lms,wrdsb/canvas-lms,sfu/canvas-lms,arrivu/qibla-ecampus,wrdsb/canvas-lms,grahamb/canvas-lms,landonwilkins/canvas-lms,Unow/canvas-lms,venturehive/canvas-lms,Unow/canvas-lms,nditech/red-innovadores-lms,djbender/canvas-lms,djbender/canvas-lms,loganrun/pincan,arrivu/jigsaw-lms,wye0220/shindig-canvas,kyroskoh/canvas-lms,Unow/ins,antoniuslin/canvas-lms,sdeleon28/canvas-lms,whalejasmine/canvas-lms,antoniuslin/canvas-lms,samuels410/greatlakes-lms,parbros/red-innovadores-lms,efrj/canvas-lms,nditech/red-innovadores-lms,sfu/canvas-lms,leftplusrightllc/canvas-lms,SwinburneOnline/canvas-lms,ShreniiNepal/shrenii_lmp,wimemx/Canvas,shidao-fm/canvas-lms,sdeleon28/canvas-lms,efrj/canvas-lms,jay3126/canvas-lms,ankithbti/canvas_lms,samuels410/greatlakes-lms,merichar/canvas-lms,wrdsb/canvas-lms,grahamb/canvas-lms,landonwilkins/canvas-lms,wye0220/shindig-canvas,sfu/canvas-lms,arrivu/arrivu-lms,sdeleon28/canvas-lms,landonwilkins/canvas-lms,nditech/red-innovadores-lms,arrivu/hoodemo