Fix JarFileTest#test_getInputStreamLjava_util_jar_JarEntry_subtest0

This failure is due to OpenJDK has different behaviour when dealing
with JarEntry in getInputStream. If argument 'entry' is of type
JarEntry, it reloads it as JarFileEntry using its file name. Therefore
setting size on 'entry' would be ignored.

We initialize entry as JarFileEntry instead, so that getInputStream sees
our change to JarEntry's size.

Bug: 25996922
Change-Id: I4976db19c4b5ddb5802a3e52af7dc9a9df85aaa1