Fix JENKINS-20215

When user doens't have a Mailer.UserProperty with the email address, just add the user id as a recipient and it will add the default suffix.

src/main/java/hudson/plugins/emailext/ExtendedEmailPublisher.java

@@ -632,7 +632,8 @@ private void addUserTriggeringTheBuild(AbstractBuild<?, ?> build, Set<InternetAd
             if (adrs != null) {
                 addAddressesFromRecipientList(recipientAddresses, ccAddresses, adrs, env, listener);
             } else {
-                listener.getLogger().println("Failed to send e-mail to " + user.getFullName() + " because no e-mail address is known, and no default e-mail domain is configured");
+                listener.getLogger().println("The user does not have a configured email address, trying the user's id");
+                addAddressesFromRecipientList(recipientAddresses, ccAddresses, user.getId(), env, listener);                
             }
         }
     }