Don't report missing source/javadoc jars when download is false

When you specify not to download -javadoc jars (or -source jars), don't report the missing jar files. Currently my console is spammed with these messages that repeat over and over in a multi-module reactor build, making it neigh impossible to see if there's a missing dependency.

The attached patch will only log missing -javadoc jars and missing -source jars when their respective flags are enabled.