Do not cherry-pick or revert commit more than once

Instead just return success. In the case that no commit has been
cherry-picked or reverted, just return the old HEAD.
    
Bug: 333814
Change-Id: I67db2b77b52c43932436d22a8daa5a6556423484
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/CherryPickCommand.java

 						JGitText.get().commitOnRepoWithoutHEADCurrentlyNotSupported);
 			RevCommit headCommit = revWalk.parseCommit(headRef.getObjectId());
 
+			newHead = headCommit;
+
 			// loop through all refs to be cherry-picked
 			for (Ref src : commits) {
 				// get the commit to be cherry-picked
 				merger.setBase(srcParent.getTree());
 
 				if (merger.merge(headCommit, srcCommit)) {
+					if (AnyObjectId.equals(headCommit.getTree().getId(), merger
+							.getResultTreeId()))
+						continue;
 					DirCacheCheckout dco = new DirCacheCheckout(repo,
 							headCommit.getTree(), repo.lockDirCache(),
 							merger.getResultTreeId());

org.eclipse.jgit/src/org/eclipse/jgit/api/RevertCommand.java

 						JGitText.get().commitOnRepoWithoutHEADCurrentlyNotSupported);
 			RevCommit headCommit = revWalk.parseCommit(headRef.getObjectId());
 
+			newHead = headCommit;
+
 			// loop through all refs to be reverted
 			for (Ref src : commits) {
 				// get the commit to be reverted
 				merger.setBase(srcCommit.getTree());
 
 				if (merger.merge(headCommit, srcParent)) {
+					if (AnyObjectId.equals(headCommit.getTree().getId(), merger
+							.getResultTreeId()))
+						continue;
 					DirCacheCheckout dco = new DirCacheCheckout(repo,
 							headCommit.getTree(), repo.lockDirCache(),
 							merger.getResultTreeId());