Fix GetDirectBufferCapacity() implementation

[koutheir]

GetDirectBufferCapacity() JNI must return -1 if the given object is not a direct java.nio.Buffer.

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[koutheir]

I already signed the OCA months ago.

[oubidar-Abderrahim]

Hi, @koutheir, Thank you for contributing to GraalVM, could you please provide answers to the following questions?

Is your PR complete and ready for review? Did you have a conversation about these changes with some team members and you would like for them to review this as they have more context? please mention them Do your changes rely on other changes made in a separate open PR? if yes please link it to this one

[koutheir]

Is your PR complete and ready for review?

Yes.

Did you have a conversation about these changes with some team members and you would like for them to review this as they have more context?

No.

Do your changes rely on other changes made in a separate open PR?

No.

[oubidar-Abderrahim]

@christianwimmer could you please assign a reviewer for this PR? Also please let me know if I should mirror it into Ol-Bitbucket? Thank you.

[koutheir]

I might have done something incorrectly. I pulled changes and merged from the master branch, and applied the same changes again in order to resolve the conflicts. Can we continue in #4838 ?

[peter-hofer]

Most likely you removed all commits in a push and that led the automation to believe that your changes were already integrated.