Preview creation checks allowed file extensions

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.1.0 CE GA1, 6.1.10 EE GA1, 6.2.0 CE M2
• Fix Version/s: 6.1.10 EE GA1, 6.1.20 EE GA2, --Sprint 11/12, 6.2.0 CE M2
• Component/s: Documents & Media
• Labels:
  • QA-R
• Branch Version/s:
  6.1.x
• Backported to Branch:
  Committed
• Fix Priority: 3
• Added to Fix Pack:
  Added
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/5269

When a preview for a document is created, the preview is being checked for a valid file extension. This is error prone and seems unnecessary:
1) When the preview is of a different file type than the original file (for instance, PDF previews won't work if .png files are not allowed).
2) When no new file uploads of a specific type are allowed, while legacy files types have to be kept in the system.