px:unzip should throw an error when it's unable to unzip (usually due to unsupported compression method)

If any of the zip entries declares a size of -1, the step should not attempt to read any of the files in the zip but should instead throw an error stating that zip could not be read, that the reason it could not be read is probably because it uses an unsupported compression method, and that the only supported compression method is currently normal deflate.

see nlbdev/nordic-epub3-dtbook-migrator#144