PayPal uc_paypal_ec_submit_form_submit() triggered on uc_cart_checkout_review_form even when using a different payment method

I have a shop supporting multiple payment methods, e.g. uc_credit module and PayPal Express Checkout. I ran into a problem where the uc_paypal_ec_submit_form_submit() function was been executed whenever the uc_cart_checkout_review_form form was submitted - even if Express Checkout was not chosen as the payment method! This caused it to send the DoExpressCheckoutPayment nvp request to PayPal, which obviously failed, as no payer id, etc was present in the request.

The attached patch changes it so that the ec submit handler is only added to the list of submit functions if the payment method chosen was "paypal_ec".