fix(q): resolve all of nothing to nothing

$q.all([]) no longer throws exception and resolves to empty array []

Author: mhevery

Diff for: src/service/q.js

@@ -364,16 +364,20 @@ function qFactory(nextTick, exceptionHandler) {
         counter = promises.length,
         results = [];
 
-    forEach(promises, function(promise, index) {
-      promise.then(function(value) {
-        if (index in results) return;
-        results[index] = value;
-        if (!(--counter)) deferred.resolve(results);
-      }, function(reason) {
-        if (index in results) return;
-        deferred.reject(reason);
+    if (counter) {
+      forEach(promises, function(promise, index) {
+        ref(promise).then(function(value) {
+          if (index in results) return;
+          results[index] = value;
+          if (!(--counter)) deferred.resolve(results);
+        }, function(reason) {
+          if (index in results) return;
+          deferred.reject(reason);
+        });
       });
-    });
+    } else {
+      deferred.resolve(results);
+    }
 
     return deferred.promise;
   }

Diff for: test/service/qSpec.js

@@ -676,6 +676,14 @@ describe('q', function() {
 
 
   describe('all', function() {
+    it('should resolve all of nothing', function() {
+      var result;
+      q.all([]).then(function(r) { result = r; });
+      mockNextTick.flush();
+      expect(result).toEqual([]);
+    });
+
+
     it('should take an array of promises and return a promise for an array of results', function() {
       var deferred1 = defer(),
           deferred2 = defer();