TypeError in Config translation plugin when configuration is renamed [#3544230]

Problem/Motivation

The Babel Config translation type plugin throws a TypeError when trying to access configuration that has been renamed, causing the translation interface to crash.

TypeError: Drupal\Component\Utility\NestedArray::getValue(): Argument #1 ($array) must be of type array, null given, called in /babel/src/Plugin/Babel/TranslationType/Config.php on line 89

Steps to reproduce

1. Create translatable configuration (e.g., a block)
2. Add translations via Babel
3. Rename the configuration (e.g., block ID changes from dash to underscore)
4. Visit /admin/config/regional/babel

Issue fork babel-3544230

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3544230-typeerror-in-config changes, plain diff MR !47
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