[Bug] Transition "cancel" is called even on completed or already canceled payment

[LucaGallinari]

SyliusPayPalPlugin version affected: >=1.3.2

Description
The "CancelLastPayPalPaymentAction" is called even when the payment page in "unloaded" due to a successful payment. This lead to call the transition "cancel" on the payment even if it's completed and results in an error like this:

Uncaught PHP Exception SM\SMException: "Transition "cancel" cannot be applied on state "completed" of object "App\Entity\Payment\Payment" with graph "sylius_payment""

Steps to reproduce

1. Place an order with a successful payment
2. You can see in the network tab or in the log (it depends on your monolog settings) that the request to "cancel-last-pay-pal-payment" failed with a 500.

Possible Solution
This is due to this. The cancel transition is called without checking if it can be run (with ->can()).
There is also this point in which this change should be applied.