HttpPluginServlet: Fix "short read of block" IO error on plugin docs

When accessing plugins static resources from the Jar, treat the
JarEntry size as a "hint" to the expected uncompressed size, rather
than the exact size.

Treating as "exact value" can result in an IO error whilst reading
the resource:

  java.io.EOFException: Short read of block

Change-Id: I6b488e58bb34620483d9ed7524ac3c23ce44071a
1 file changed