[MPIR-279] Wrong hyperlinks on index and modules page

* Write a default module name when no one is in the model.
  Same behavior as in DefaultSiteTool

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/branches/MPIR-279@1636171 13f79535-47bb-0310-9956-ffa450edef68