unhandled exception and EInOutError for read-only input file

[rbw42]

On linux, using either pre-compiled or self-compiled code.
The code fails with:
An unhandled exception occurred at $0000000000402525: EInOutError: Access denied $0000000000402525
If the input file doesn't have write permissions for the user, even though it doesn't seem to need write permissions. (Didn't modify the size or timestamp on the input file as best I can tell.)