Collaboration file extension check is case sensitive

[kobergj]

Describe the bug

When checking file extension collaboration service will check case sensitive. That means it will not open .PPTX files even though it opens .pptx files just fine.

Steps to reproduce

1. Upload or create a test.pptx file (for example, extension doesn't matter)
2. Rename it to test.PPTX
3. Open it in OnlyOffice

Expected behavior

The file opens normally

Actual behavior

An error occurs

Setup

Needs a weboffice (e.g. OnlyOffice) to see the error.