Fixed source repository and issue tracking url's being added to nav even if the elements in the pom were empty

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@114149 13f79535-47bb-0310-9956-ffa450edef68

xdoc/src/plugin-resources/navigation.jelly

@@ -16,11 +16,13 @@
               <item name="Project Team" href="/team-list.html"/>
               <item name="Dependencies" href="/dependencies.html"/>
               
-              <j:if test="${!empty(pom.repository.url)}">
+              <j:set var="url" value="${pom.repository.url}"/>
+              <j:if test="${!empty(url)}">
                 <item name="Source Repository" href="/cvs-usage.html"/>
               </j:if>
                 
-              <j:if test="${!empty(pom.issueTrackingUrl)}">
+              <j:set var="url" value="${pom.issueTrackingUrl}"/>
+              <j:if test="${!empty(url)}">
                 <item name="Issue Tracking" href="/issue-tracking.html"/>
               </j:if>
             </item>