Uploading a password-protected .xlsb workbook without its password
answered 500 with the unattributable-failure message instead of 400 with
the remedy.
DetectPasswordProtection in pkg/modules/libreoffice/api/protection.go
infers encryption from a compound-file header carried by an extension
whose unencrypted form is always a ZIP package. The ooxmlExtensions map
listed .xlsx, .xlsm, .xltx and .xltm but not .xlsb, so an encrypted
workbook under that extension fell through to PasswordProtectionUnknown.
The convert route in pkg/modules/libreoffice/routes.go then matched
neither password branch of its exit-code switch and returned the 500
default.
An Excel Binary Workbook is an Open Packaging Conventions ZIP holding
binary parts, so a compound file under that extension is encrypted for
the same reason .xlsx is. Adding .xlsb to the map restores the 400 that
names the 'password' form field.
