Fix WooCommerce settings losing saved Worldpay credentials

[ginozzzz]

This updates the packaged WooCommerce plugin to preserve configured Worldpay credentials and identifiers when WooCommerce submits masked or blank settings fields.

Root cause

A blank password field could be returned by the validator and overwrite a valid saved password during settings save. The credential test could also read blank browser fields instead of persisted values.

Change

• Preserve configured values on blank submissions.
• Resolve Try versus Live validation from the submitted mode.
• Fall back to persisted username and checkout ID during credential tests.
• Refresh persisted gateway settings before rendering.
• Add administrator guidance to leave unchanged saved credentials blank.

Validation

• Patch applies cleanly to the v1.3.3 package.
• PHP lint passes for all changed PHP files.
• Local no-provider regression probe passes for onsite and offsite gateways.
• Focused OMS Worldpay tests pass: 20 tests, 64 assertions.

The committed change is the v1.3.3 distribution ZIP in EmbeddedCheckout/Woocommerce/worldpay-ecommerce-woocommerce.zip.