IOUtils.isEmpty() doesn't reinclude byte in stream.

While trying to integrate Katharsis with CXF I faced a problem related to IOUtils.isEmpty() method.

When isEmpty is invoked with an InputStream that:
1. Is not 'mark supported' and
2. The 'available()' method returns '0'.

The byte that is read from the stream (used to determine whether the stream is empty or not) is not re-included back to the stream. When I explored the code inside PushbackInputStream class, I found that the byte is only being included inside the PushbackInputStream.buf (using unread(byte[], int, int) method).

Find attached Maven Project containing 2 test cases.

References:
> IOUtils: https://cxf.apache.org/javadoc/latest/org/apache/cxf/helpers/IOUtils.html
> PushbackInputStream: https://docs.oracle.com/javase/7/docs/api/java/io/PushbackInputStream.html
> Katharsis.io: http://katharsis.io