fix conversation attachments in IE, closes #5700
fix conversation attachments in IE, closes #5700

Change-Id: Ie6bedbe266ef6e49b825adab0b0bb635e1ccd919
Reviewed-on: https://gerrit.instructure.com/5746
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>
Reviewed-by: Zach Pendleton <514dbb4d54d4f29e454990df7d075678f43f92aa@instructure.com>
Reviewed-by: Jacob Fugal <f862f167b85d41b225785c70d70808bc7337c1fe@instructure.com>

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