FOP_CreateFormOfPayment allow sequence number 0

[therealartz]

Fop sequence number check must be changed, because empty() method returns false, when $sequenceNr = 0.
It breaks the struct when trying to add a form of payment (FP) element including both old and new forms of payment where old must have 0 sequence number
(First example on FOP_CreateFormOfPayment examples page at extranet)

<fopSequenceNumber>
    <sequenceDetails>
        <number>0</number>
    </sequenceDetails>
</fopSequenceNumber>

[coveralls]

Coverage remained the same at 99.851% when pulling 1cbb393 on therealartz:fix/fop-sequence-number into 991f4d4 on amabnl:master.

[DerMika]

I would prefer if (!is_null($options->sequenceNr)) instead of isset, because the option should always be set in the request options object.

[DerMika]

Thanks for contributing!

[DerMika]

Version 1.7.0 has just been released!