don't error out if a stream item's assignment is hard deleted
don't error out if a stream item's assignment is hard deleted

Change-Id: I1b7976a68b5e2bebf7fe6b5d7db065024e3141ec
Reviewed-on: https://gerrit.instructure.com/5317
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

greyhwndz/canvas-lms,antoniuslin/canvas-lms,efrj/canvas-lms,dgynn/canvas-lms,arrivu/hiring-site,rup/Tarrax,grahamb/canvas-lms,landonwilkins/canvas-lms,shidao-fm/canvas-lms,em2/canvas-lms,HotChalk/canvas-lms,ShreniiNepal/shrenii_lmp,arrivu/hoodemo,eCNAP/CANVAS,skmezanul/canvas-lms,juoni/canvas-lms,sfu/canvas-lms,parbros/red-innovadores-lms,em2/canvas-lms,icelab/canvas,skmezanul/canvas-lms,eCNAP/CANVAS,fronteerio/canvas-lms,efrj/canvas-lms,usmschuck/canvas,arrivu/hiring-site,samuels410/greatlakes-lms,jay3126/canvas-lms,venturehive/canvas-lms,samuels410/greatlakes-lms,ottenhoff/canvas-lms,skmezanul/canvas-lms,Jyaasa/canvas-lms,wrdsb/canvas-lms,samuels410/greatlakes-lms,narigone/canvas,roxolan/canvas-lms,icelab/canvas,tgroshon/canvas-lms,AndranikMarkosyan/lms,HotChalk/canvas-lms,antoniuslin/canvas-lms,arrivu/qibla-ecampus,grahamb/canvas-lms,wrdsb/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,leftplusrightllc/canvas-lms,faraazkhan/canvas,SwinburneOnline/canvas-lms,Unow/ins,antoniuslin/canvas-lms,jay3126/canvas-lms,va7map/canvas-lms,leftplusrightllc/canvas-lms,arrivu/jigsaw-lms,Jyaasa/canvas-lms,fronteerio/canvas-lms,landonwilkins/canvas-lms,sfu/canvas-lms,va7map/canvas-lms,wimemx/Canvas,Unow/canvas-lms,loganrun/pincan,efrj/canvas-lms,jay3126/canvas-lms,djbender/canvas-lms,utkarshx/canvas-lms,eCNAP/CANVAS,whalejasmine/canvas-lms,shidao-fm/canvas-lms,Rvor/canvas-lms,venturehive/canvas-lms,kyroskoh/canvas-lms,HotChalk/canvas-lms,snehakachroo1/LSI_replica,snehakachroo1/LSI_replica,nditech/red-innovadores-lms,utkarshx/canvas-lms,sfu/canvas-lms,faraazkhan/canvas,djbender/canvas-lms,sfu/canvas-lms,arrivu/jigsaw-lms,djbender/canvas-lms,sfu/canvas-lms,em2/canvas-lms,efrj/canvas-lms,HotChalk/canvas-lms,merichar/canvas-lms,Unow/ins,venturehive/canvas-lms,redconfetti/canvas-lms,Rvor/canvas-lms,tgroshon/canvas-lms,roxolan/canvas-lms,matematikk-mooc/canvas-lms,sli7246/canvas_branch,ottenhoff/canvas-lms,ankithbti/canvas_lms,wye0220/shindig-canvas,kyroskoh/canvas-lms,eCNAP/CANVAS,arrivu/arrivu-lms,skmezanul/canvas-lms,fronteerio/canvas-lms,tgroshon/canvas-lms,arrivu/hoodemo,grahamb/canvas-lms,shidao-fm/canvas-lms,instructure/canvas-lms,Unow/canvas-lms,dgynn/canvas-lms,arrivu/arrivu-lms,Unow/ins,whalejasmine/canvas-lms,parbros/red-innovadores-lms,sdeleon28/canvas-lms,narigone/canvas,instructure/canvas-lms,wye0220/shindig-canvas,usmschuck/canvas,Unow/canvas-lms,tgroshon/canvas-lms,djbender/canvas-lms,va7map/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,sdeleon28/canvas-lms,instructure/canvas-lms,snehakachroo1/LSI_replica,redconfetti/canvas-lms,dgynn/canvas-lms,AndranikMarkosyan/lms,ShreniiNepal/shrenii_lmp,instructure/canvas-lms,arrivu/hoodemo,merichar/canvas-lms,samuels410/greatlakes-lms,merichar/canvas-lms,ShreniiNepal/shrenii_lmp,snehakachroo1/LSI_replica,sfu/canvas-lms,matematikk-mooc/canvas-lms,sdeleon28/canvas-lms,antoniuslin/canvas-lms,AndranikMarkosyan/lms,arrivu/qibla-ecampus,grahamb/canvas-lms,AndranikMarkosyan/lms,arrivu/qibla-ecampus,SwinburneOnline/canvas-lms,matematikk-mooc/canvas-lms,utkarshx/canvas-lms,gbleydon/canvas-lms,kyroskoh/canvas-lms,instructure/canvas-lms,roxolan/canvas-lms,nditech/red-innovadores-lms,loganrun/pincan,leftplusrightllc/canvas-lms,gbleydon/canvas-lms,Jyaasa/canvas-lms,loganrun/pincan,arrivu/jigsaw-lms,greyhwndz/canvas-lms,whalejasmine/canvas-lms,venturehive/canvas-lms,fronteerio/canvas-lms,grahamb/canvas-lms,rup/Tarrax,va7map/canvas-lms,redconfetti/canvas-lms,sli7246/canvas_branch,matematikk-mooc/canvas-lms,wimemx/Canvas,SwinburneOnline/canvas-lms,Rvor/canvas-lms,icelab/canvas,sdeleon28/canvas-lms,greyhwndz/canvas-lms,wrdsb/canvas-lms,whalejasmine/canvas-lms,Jyaasa/canvas-lms,instructure/canvas-lms,juoni/canvas-lms,narigone/canvas,faraazkhan/canvas,landonwilkins/canvas-lms,jay3126/canvas-lms,arrivu/hiring-site,usmschuck/canvas,usmschuck/canvas,gbleydon/canvas-lms,juoni/canvas-lms,ottenhoff/canvas-lms,wye0220/shindig-canvas,sli7246/canvas_branch,dgynn/canvas-lms,shidao-fm/canvas-lms,arrivu/arrivu-lms,wimemx/Canvas,greyhwndz/canvas-lms,nditech/red-innovadores-lms,landonwilkins/canvas-lms,leftplusrightllc/canvas-lms,wrdsb/canvas-lms,redconfetti/canvas-lms,ankithbti/canvas_lms,ankithbti/canvas_lms,utkarshx/canvas-lms,Rvor/canvas-lms,rup/Tarrax,kyroskoh/canvas-lms,narigone/canvas,SwinburneOnline/canvas-lms,nditech/red-innovadores-lms,ShreniiNepal/shrenii_lmp,parbros/red-innovadores-lms