Amount is null if label for the amount field is set

Hi,

Thanks for providing an highly configurable widget for free :).

With the latest update v5.6.3, if I set an label for the amount field, the fixed price is null instead of the amount I set earlier.

Steps to reproduce:
1. Go here /wp-admin/options-general.php?page=quick-paypal-payments%2Fsettings.php&tab=settings
2. Specify a fixed amount €50 for eg.
3. Untick “Do not validate”
4. Tick “Display as a pre-set amout”
5. Option selector: Radio
6. Tick “Display inline radio fields”
7. Untick “Add input field to dropdown”
8. In “Fixed payment and shortcode labels” section, set a label for the payment Reference/ID/Number: “Payment for:” (for eg).
9. Set a label for the amount field: “Amount:” (for eg).

Expected:
In the Paypal form heading, I should see:
<Paypal Heading>
<blurb>
Payment for: blablabla
Amount: €50.00
[…]

Currently:
In the Paypal form heading, I see:
<Paypal Heading>
<blurb>
Payment for: blablabla
Amount: €0.00
[…]

If I do not set a label for the amount field, I see:
<Paypal Heading>
<blurb>
Payment for: blablabla
€50.00
[…]

Thanks for helping me on that bug introduced in plugin version 5.6.3. I worked just before.

KR,
TheBigWorld