Fix FileTreeIterator.idSubmodule(Entry)

FileTreeIterator was calling by mistake
WorkingTreeIterator.idSubmodule(Entry). Instead it should always compute
idSubmodule on its own.

Change-Id: Id1b988aded06939b1d7edd2671e34bf756896c0e

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/IndexDiffSubmoduleTest.java

@@ -87,7 +87,7 @@ public class IndexDiffSubmoduleTest extends RepositoryTestCase {
 				.call();
 
 		submodule_db = (FileRepository) Git.wrap(db).submoduleAdd()
-				.setPath("submodule")
+				.setPath("modules/submodule")
 				.setURI(submoduleStandalone.getDirectory().toURI().toString())
 				.call();
 		submoduleStandalone.close();

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/FileTreeIterator.java

@@ -67,8 +67,8 @@ import org.eclipse.jgit.util.FS;
  */
 public class FileTreeIterator extends WorkingTreeIterator {
 	/**
-	 * the starting directory. This directory should correspond to the root of
-	 * the repository.
+	 * the starting directory of this Iterator. All entries are located directly
+	 * in this directory.
 	 */
 	protected final File directory;
 
@@ -238,8 +238,6 @@ public class FileTreeIterator extends WorkingTreeIterator {
 
 	@Override
 	protected byte[] idSubmodule(final Entry e) {
-		if (repository == null)
-			return idSubmodule(getDirectory(), e);
-		return super.idSubmodule(e);
+		return idSubmodule(getDirectory(), e);
 	}
 }