Fix resolution of tree when path is empty

Revision strings that end with a ':' with no trailing path
should return the tree associated with the current ref parsed

Bug: 368370
Change-Id: I7c7617a77bd418bad4e570be2d1e9002ad280762
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

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

@@ -218,6 +218,10 @@ public class RepositoryResolveTest extends SampleDataRepositoryTestCase {
 
 		assertEquals(b2_txt, db.resolve("b:b/b2.txt"));
 		assertEquals(b_root, db.resolve("b:"));
+		assertEquals(id("6020a3b8d5d636e549ccbd0c53e2764684bb3125"),
+				db.resolve("master:"));
+		assertEquals(id("10da5895682013006950e7da534b705252b03be6"),
+				db.resolve("master:b/b2.txt"));
 		assertEquals(master_txt, db.resolve(":master.txt"));
 		assertEquals(b3_b2_txt, db.resolve("b~3:b/b2.txt"));
 

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

@@ -560,7 +560,7 @@ public abstract class Repository {
 					tree = rw.parseTree(ref);
 				}
 
-				if (i == rev.length - i)
+				if (i == rev.length - 1)
 					return tree.copy();
 
 				TreeWalk tw = TreeWalk.forPath(rw.getObjectReader(),