Column menu repositioning throws exception when second column menu button is clicked

[c0bra]

To reproduce:

1. Go to the sorting tutorial (http://ui-grid.info/docs/#/tutorial/102_sorting)
2. Click on the left-most column's menu button, the menu will show.
3. Click on any other column's menu button.

You will get an exception in your console like so:

TypeError: Cannot read property 'lastMenuWidth' of undefined
    at Object.service.repositionMenu (http://ui-grid.info/release/ui-grid-unstable.js:430:31)
    at Scope.$scope.showMenu (http://ui-grid.info/release/ui-grid-unstable.js:517:35)
    at Scope.$scope.toggleMenu (http://ui-grid.info/release/ui-grid-unstable.js:896:46)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:10567:21
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:18627:17
    at Scope.$eval (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:12412:28)
    at Scope.$apply (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:12510:23)
    at HTMLDivElement.<anonymous> (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:18626:21)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:2780:10
    at forEach (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.js:330:20) 

It is probably happening because since the column's menu has not been shown yet, it has no lastMenuWidth property defined. There probably needs to be a typeof($scope.col.lastMenuWidth) === 'undefined' || $scope.col.lastMenuWidth === null check, or something like that.