fix(validate-token): gracefully handle empty data response

dist/ng-token-auth.js

@@ -509,7 +509,7 @@ angular.module('ng-token-auth', ['ipCookie']).provider('$auth', function() {
                     $rootScope.$broadcast('auth:validation-error', data);
                     return _this.rejectDfd({
                       reason: 'unauthorized',
-                      errors: data.errors
+                      errors: data != null ? data.errors : ['Unspecified error']
                     });
                   };
                 })(this));

src/ng-token-auth.coffee

@@ -585,7 +585,7 @@ angular.module('ng-token-auth', ['ipCookie'])
 
                   @rejectDfd({
                     reason: 'unauthorized'
-                    errors: data.errors
+                    errors: if data? then data.errors else ['Unspecified error']
                   })
                 )
             else

test/test/unit/ng-token-auth/token-handling.coffee

@@ -238,3 +238,21 @@ suite 'token handling', ->
       $auth.validateUser()
       $timeout.flush()
       assert.equal(null, $auth.retrieveData('auth_headers'))
+
+  suite 'empty response', ->
+    setup ->
+      $auth.getConfig().forceValidateToken = true
+      $httpBackend
+        .expectGET('/api/auth/validate_token')
+        .respond(401, undefined)
+
+      dfd = $auth.validateUser()
+
+      $httpBackend.flush()
+
+    test 'promise should be rejected without error', (done) ->
+      dfd.catch(->
+        assert true
+        done()
+      )
+      $timeout.flush()