Revise conditions under which dojo/when creates a promise; fixes #166…

…67 in trunk !strict

git-svn-id: http://svn.dojotoolkit.org/src/dojo/trunk@30605 560b804f-0ae3-0310-86f3-f6aa0a117693

tests/when.js

@@ -14,6 +14,12 @@ define([
 			t.t(this.deferred.promise === promise2);
 		},
 
+		"when() doesn't convert to promise if errback is passed but no callback": function(t){
+			var obj = {};
+			var result = when(obj, null, function(){});
+			t.t(result === obj);
+		},
+
 		"when() with a result value": function(t){
 			var obj = {};
 			var received;

when.js

@@ -36,8 +36,8 @@ define([
 		var nativePromise = receivedPromise && valueOrPromise instanceof Promise;
 
 		if(!receivedPromise){
-			if(callback){
-				return callback(valueOrPromise);
+			if(arguments.length > 1){
+				return callback ? callback(valueOrPromise) : valueOrPromise;
 			}else{
 				return new Deferred().resolve(valueOrPromise);
 			}