Fix NPE when WorkingTreeIterator does not have a repository set

It's strange that we have that member since it is not so clear
when it it set or not.

Change-Id: I53903a264f46866d249901a3cd9f9295028aa6bd
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.java7.test/src/org/eclipse/jgit/treewalk/FileTreeIteratorJava7Test.java

@@ -114,7 +114,8 @@ public class FileTreeIteratorJava7Test extends RepositoryTestCase {
 		assertEquals("link", dci.getEntryPathString());
 
 		// test
-		assertFalse(fti.isModified(dci.getDirCacheEntry(), true));
+		assertFalse(fti.isModified(dci.getDirCacheEntry(), true,
+				db.newObjectReader()));
 	}
 
 	/**
@@ -195,6 +196,7 @@ public class FileTreeIteratorJava7Test extends RepositoryTestCase {
 		assertEquals("link", dci.getEntryPathString());
 
 		// test
-		assertTrue(fti.isModified(dci.getDirCacheEntry(), true));
+		assertTrue(fti.isModified(dci.getDirCacheEntry(), true,
+				db.newObjectReader()));
 	}
 }

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

@@ -922,7 +922,8 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		} else {
 			if (mode == FileMode.SYMLINK.getBits())
 				return !new File(readContentAsNormalizedString(current()))
-						.equals(new File((readContentAsNormalizedString(entry))));
+						.equals(new File((readContentAsNormalizedString(entry,
+								reader))));
 			// Content differs: that's a real change, perhaps
 			if (reader == null) // deprecated use, do no further checks
 				return true;
@@ -971,9 +972,9 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		}
 	}
 
-	private String readContentAsNormalizedString(DirCacheEntry entry)
+	private static String readContentAsNormalizedString(DirCacheEntry entry,
-			throws MissingObjectException, IOException {
+			ObjectReader reader) throws MissingObjectException, IOException {
-		ObjectLoader open = repository.open(entry.getObjectId());
+		ObjectLoader open = reader.open(entry.getObjectId());
 		byte[] cachedBytes = open.getCachedBytes();
 		return FS.detect().normalize(RawParseUtils.decode(cachedBytes));
 	}