Consolidate pagination metadata nil pointer checks

[PaulSonOfLars]

Description

Consolidate pagination metadata nil pointer checks, fixing a panic in the region availability lists (#408)

Related Issues

Fixes #408

Checklist:

• [Y] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [Y] Have you linted your code locally prior to submission?
• [Y] Have you successfully ran tests with your changes locally?

[github-actions]

Unit Tests and Coverage

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?   	github.com/vultr/vultr-cli/v3	[no test files]

Pusher: @PaulSonOfLars, Action: pull_request_target

[optik-aper]

@PaulSonOfLars I like what you're doing here. Thanks for submitting the PR. I'm gonna look at this more closely and think it through. It's probably going to need a rebase once my PR goes in, so if you want to hold off to push the lint fixes until then, that'd be swell.

[PaulSonOfLars]

@optik-aper no problem!
Sure thing, let me know when your PR is in and I'll rework this one

[optik-aper]

Just merged it!

[github-actions]

Unit Tests and Coverage

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?   	github.com/vultr/vultr-cli/v3	[no test files]

Pusher: @PaulSonOfLars, Action: pull_request_target

[github-actions]

Unit Tests and Coverage

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?   	github.com/vultr/vultr-cli/v3	[no test files]

Pusher: @PaulSonOfLars, Action: pull_request_target

[github-actions]

Unit Tests and Coverage

Show Output

?   	github.com/vultr/vultr-cli/v3	[no test files]

Pusher: @PaulSonOfLars, Action: pull_request_target

[optik-aper]

This seems a little redundant but I think this is a good safety mechanism to check for nil structs. I'm merging it and might tweak it in the future. Thanks for the PR