Check that all categories in a given list are valid category objects.

@param  {Array} categories List of categories from the remote site API
@return {Boolean}          True if the categories are valid.
function isValidCategoriesArray( categories ) {
	for ( let i = 0; i < categories.length; i++ ) {
		if ( ! isValidProductCategory( categories[ i ] ) ) {
			// Short-circuit the loop and return now.
			return false;
		}
	}
	return true;
}