CORS error triggers an undefined TypeError when using typescript-fetch

Description

openapi-generator version

I'm using 6.0.0.jar

Command line used for generation

          npx @openapitools/openapi-generator-cli generate \
              -i ./openapi/my.sdk.yaml \
              --additional-properties npmVersion=1.0.${{ github.run_number }}rc${{ github.event.number }} \
              -g typescript-fetch \
              --config ./openapi/openapi-typescript-config.json \
              -o ts-fetch-client

Steps to reproduce

Your API that you are using takes a vacation and doesn't respond to OPTIONS requests. It returns 404 instead.
When this happens, this line generates a TypeError due to response being: undefined
https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache#L108

Related issues/PRs

I couldn't find one

Suggest a fix/enhancement

I have a PR

Start with modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache at line 108, then reproduce using the provided generator command against an API that returns 404 for OPTIONS requests. Done means the generated typescript-fetch client no longer throws an undefined TypeError in this CORS failure case; verify with the relevant runtime tests if available.