Function pmd_pkdpx::is_px

pub fn is_px<F: Read + Seek>(file: &mut F) -> Result<bool, PXError>

check if a file is a px-compressed filed (PKDPX or AT4PX) . return true if it is one, false otherwise.

It doesn't do extensive test and don't guaranty that the file is a valid PKDPX (only check the header) Also doesn't save the position of the cursor in the file