A fuzzed signed jar throws an exception when retrieving the
manifest entry, this seems to be due to a miscalculated offset while UTF8
decoding:

java JarTest iae_malformat_input.jar
Exception in thread "main" java.lang.IllegalArgumentException: malformed
input off : 80, length : 1
at java.base/java.lang.StringCoding.throwMalformed(StringCoding.java:698)
at java.base/java.lang.StringCoding.decodeUTF8_0(StringCoding.java:885)
at
java.base/java.lang.StringCoding.newStringUTF8NoRepl(StringCoding.java:978)
at java.base/java.lang.System$2.newStringUTF8NoRepl(System.java:2273)
at java.base/java.util.zip.ZipCoder$UTF8ZipCoder.toString(ZipCoder.java:208)
at java.base/java.util.zip.ZipFile.getZipEntry(ZipFile.java:671)
at java.base/java.util.zip.ZipFile.getEntry(ZipFile.java:330)
at java.base/java.util.jar.JarFile.getManEntry(JarFile.java:935)
at
java.base/java.util.jar.JarFile.getManifestFromReference(JarFile.java:417)
at java.base/java.util.jar.JarFile.getManifest(JarFile.java:409)
at JarTest.main(JarTest.java:12)
Caused by: java.nio.charset.MalformedInputException: Input length = 1