Dashboard/Gridster on mobile bug

Wrong width calculation on mobile devices because

jQuery(".mainContainer").length === 0

see: layouts\v7\modules\Vtiger\resources\DashBoard.js:305

fix would be:

-- var col_width = (cols === 1)?(Math.floor(($(".mainContainer").width()-41)/cols) - (2*widgetMargin)):(Math.floor(($(window).width()-41)/cols) - (2*widgetMargin));
++ var col_width = (Math.floor(($(window).width()-41)/cols) - (2*widgetMargin));

because dashboard is always full size.

If someone can confirm I would do a pull request