[lint] Check for nil pointers in CadenceV1Analyzer type annotation inspection

[jribbink]

Description

Adds missing checks for nil pointer dereferences when traversing type annotations.

Ran into this issue in CI for https://github.com/onflow/cadence-tools/pull/286

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• [x] Targeted PR against master branch
• [ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• [x] Code follows the standards mentioned here
• [x] Updated relevant documentation
• [x] Re-reviewed Files changed in the Github PR explorer
• [x] Added appropriate labels