IndexDiff: Simplify allocation of filter list

We add either 3 or 4 filters.  If we are adding only 3 filters,
allocating the array for 4 isn't a huge waste of memory, but it
does simplify our code.

Change-Id: I7df29b414f6d5cfcf533edb1405083e6fcec32cf
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java

@@ -177,8 +177,7 @@ public class IndexDiff {
 			treeWalk.addTree(new EmptyTreeIterator());
 		treeWalk.addTree(new DirCacheIterator(dirCache));
 		treeWalk.addTree(initialWorkingTreeIterator);
-		Collection<TreeFilter> filters = new ArrayList<TreeFilter>(
+		Collection<TreeFilter> filters = new ArrayList<TreeFilter>(4);
-				filter == null ? 3 : 4);
 		if (filter != null)
 			filters.add(filter);
 		filters.add(new NotIgnoredFilter(WORKDIR));