This affects #2335, at least for documents covered by `validDjvuFile()` (see 76cef07c07/frontend/document/djvudocument.lua (L15-L23)). However, that's only with regard to `touch invalid.djvu` and should not affect whatever happened in the OP.
76cef07c07/frontend/document/djvudocument.lua (L15-L23)