Steps to reproduce:

• create an image file with a 2 letter filename, e.g. use the attached "p1.png"
• upload this file to the DAM (everything's fine so far)
• select this file in some dialog (e.g. component dialog)
  => the file will not be displayed in the preview
  => the log will show a NPE

When you debug this, you'll see that the problem in fact is not a NPE, but "java.lang.IllegalArgumentException: Prefix string too short" on DamFilePreviewComponent line 163.

Workaround: Once you make sure, that the filename of the temp file is at least 4 letters long, things work fine. The attached patch does this, but it might not be the prettiest way...