Review Request JDK-8166846: jdeps fails to generate module info if there is any class in unnamed package

[Mandy Chung]

http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8166846/webrev.00/

This improves jdeps error message to indicate that a JAR file containing 
unnamed package is not valid to generate module-info.java.

Mandy