Only set location in BuildException if the task didn't provide it

before.

This will give the correct location for errors in build files invoked
via the <ant> task.


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@268007 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/Target.java

@@ -144,7 +144,10 @@ public class Target {
 		}
                 catch(RuntimeException exc) {
                     if (exc instanceof BuildException) {
-                        ((BuildException)exc).setLocation(task.getLocation());
+                        BuildException be = (BuildException) exc;
+                        if (be.getLocation() == Location.UNKNOWN_LOCATION) {
+                            be.setLocation(task.getLocation());
+                        }
                     }
                     project.fireTaskFinished(task, exc);
                     throw exc;