fix height issue with file previews

fixes CNVS-17229
Fixes the height issues in previews for ie and chrome
Test Plan
Given you have many files you can preview
And New files are enabled
When you go to new files
And you preview a file in chrome/ie/safari/ff
Then the previewed image should be centered
Then try a video, it should be centered in middle of page
Then try something that does not have a preview
it should look like: http://cl.ly/image/1m292g3i2q05
Change-Id: I2c8d88b88474ab07ee04c001d975c5332b2eda86
Reviewed-on: https://gerrit.instructure.com/45245
Reviewed-by: Dan Minkevitch <dan@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>