Do not fail on JAR archives containing invalid members with a .jar extension

_jar_normalize_member() in the JAR handler calls
File::StripNondeterminism::handlers::zip::normalize_member for every archive
member with a .jar extension. If the member is not a valid archive (e.g.
because it is just an empty file), this leads to a hard failure "Reading ZIP
archive failed" in the ZIP handler.

To solve this, extend normalize_member() in the ZIP file to detect the file
type if no $normalizer is explicitly specified. This uses
get_normalizer_for_file(), which looks at both the file extension and the
"file" command to detect the type more accurately. Therefore we need to
preserve the name of the extracted temporary file instead of just calling it
"member".

With this change in place, we can leave the normalizer for files with a .jar
extension unspecified in _jar_normalize_member(). This way if the file is not
an archive, it will get skipped by get_normalizer_for_file() and a warning will
be printed instead of a fatal error.