Improve totals reading at PaymentPaypal/Model/Abstract.php

[vovayatsyuk]

http://axiscommerce.com/forum/paypal-express-error#comment-91151

A lot of code is used direct reading of collects, but they could be undefined, which will produce an error.

For example:

    $optionsST['TAXAMT']      = round(
        $this->getAmountInBaseCurrency(
            $orderTotals['tax']['total'] + $orderTotals['shipping_tax']['total']
        ),
        2
    );

    $orderTotals['shipping_tax']['total'] - could be undefined

This code should be changed to

getTotal()->getTotal('shipping_tax') - should return float number