Fix redundant null check warning in Repository

rev is always null because of `if (rev != null) return ...` above.

Change-Id: I8168aefd344e0c4b0c68caea1a3daee66c07173b

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

@@ -697,7 +697,7 @@ public abstract class Repository {
 			return rev.copy();
 		if (name != null)
 			return name;
-		if (rev == null && done == revstr.length())
+		if (done == revstr.length())
 			return null;
 		name = revstr.substring(done);
 		if (!Repository.isValidRefName("x/" + name))