No file viewer drop-down when viewing files with extension in upper case (BB-15840)

This issue occurs when using the File Viewer add-on.

Expected behavior:
When viewing a file in the Source tab, if that file can be viewed in one of the viewers included in the add-on, the file viewer drop-down is displayed on the panel:

If a file can't be viewed in one of add-on's viewers, the file viewer drop-down is not displayed.

The issue:
If a file has extension typed in upper case and it's format is supported by the File Viewer add-on, the file viewer drop-down is not displayed, while it is expected that it would be displayed.

The add-on doesn't control when this drop-down is displayed. It is controlled by Bitbucket.

Can you make checking file extension case insensitive?