RFR: 8215291: Broken links when generating from project without modules

[Hannes Wallnöfer]

Please review:

Bug: https://bugs.openjdk.java.net/browse/JDK-8215291
Webrev: http://cr.openjdk.java.net/~hannesw/8215291/webrev.00/

No test for this functionality, but I’ve tested it manually with multiple 
sources.

Hannes