[Android] Empty icon for Preprint items

mjthoraval

I can see this:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/pc1geeouxb0q1k9od8zn.png
Instead of this on the desktop app:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/7zezw6zemiddp9u4vfmy.png

Android version: 1.0.0-51