Don't die if the ant.file property hasn't been set.

Jelly's Ant tag library currently doesn't set this property and each
<ant> task used in Jelly will result in an NPE otherwise.


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@276290 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/Ant.java

@@ -321,11 +321,13 @@ public class Ant extends Task {
                     + " in build file " +  antFile, Project.MSG_VERBOSE);
             newProject.setUserProperty("ant.file" , antFile);
 
+            String thisAntFile = getProject().getProperty("ant.file");
             // Are we trying to call the target in which we are defined (or
             // the build file if this is a top level task)?
-            if (newProject.resolveFile(newProject.getProperty("ant.file"))
-                .equals(getProject().resolveFile(getProject()
-                .getProperty("ant.file"))) && getOwningTarget() != null) {
+            if (thisAntFile != null
+                && newProject.resolveFile(newProject.getProperty("ant.file"))
+                .equals(getProject().resolveFile(thisAntFile)) 
+                && getOwningTarget() != null) {
 
                 if (getOwningTarget().getName().equals("")) {
                     if (getTaskName().equals("antcall")) {