close temp files after upload

CNVS-11519

this fixes an error introduced in 
https://gerrit.instructure.com/#/c/28234/

test plan:
-try to upload a zipped directory containing lots
of files (for example, there is a dropbox link in
CNVS-11519 containing a file you can use
-while the upload is still in progress, try to upload
the same in a different course
-check that all files are uploaded, in each course

Change-Id: I373dfebe5dbc1f21e681d35e227037cb4a316676
Reviewed-on: https://gerrit.instructure.com/31933
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Anthus Williams <awilliams@instructure.com>