Fix accessing first element of nil array in upload_price_tier

[lanpau]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

Resolves #21199

Description

Error "undefined method `first' for nil:NilClass" indicates attempting to treat nil as an array. Adding pre-condition to check if the array is not nil fixes that. Also the startDate attribute of the resource appPrices in spaceship does not exist anymore and must be removed.

Testing Steps

Calling the deliver action for apps with unspecified prices now works as expected.

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[markmuniz]

Any chance this MR can get into a release soon? We are unable to distribute apps on 2.212.2 due to this issue. Downgrading to 2.212.1 is our only workaround for now.

[vincentisambart]

This can be shortened to the following:

Suggested change

	if app_prices && app_prices.first
	if app_prices&.first

However, I don't think it is the correct fix. It seems app.prices is nil even on already released app, so you would end up always going in the else branch of this if, even if App Store Connect does have prices.
As mentioned in #21187, proper support for the new prices API is needed.

[lanpau]

I agree, this fix is not a proper way of handling broken upload_price_tier. Also, the workaround in #21199 works well enough.