Fix nil pointer dereference in backend state migration

[Mark-C-Hall]

Summary

Fixes a nil pointer dereference crash that occurs during terraform init -migrate-state when the destination backend returns an error other than ErrDefaultWorkspaceNotSupported.

Root Cause: In meta_backend_migrate.go, when StateMgr() returns an error, the code only handles ErrDefaultWorkspaceNotSupported in the if-branch. For any other error (e.g., 403 permission denied), destinationState remains nil, and the subsequent call to destinationState.RefreshState() causes a panic.

Fix: Added an else clause to return the error immediately for any non-workspace-related errors, preventing the nil pointer dereference.

Fixes #38027

Test Plan

1. Configure a GCS backend where you have permission to create the bucket but not write to it
2. Run terraform init to create local state
3. Run terraform init -migrate-state
4. Before fix: Crash with panic: runtime error: invalid memory address or nil pointer dereference
5. After fix: Clean error message: Error loading state: googleapi: Error 403: ... does not have storage.objects.list access

Related Issues

• Terraform crashes with nil pointer dereference during backend migration when permission errors occur #38027 - The issue filed for this bug
• Terraform crashed when change backend from s3 to oss #24100 - Similar crash reported for OSS backend (different code path but same pattern)

🤖 Generated with Claude Code

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[crw]

Thanks for this submission! I will raise it in triage if it is not handled before then.

[radeksimko]

The implementation looks good to me, as I mentioned in the linked issue. I have raised some further changes (#38033) that should enable us to test this scenario more thoroughly and prevent similar issues in the future. I will let that PR be reviewed first by other maintainers and come back to this.

Thank you for the fix and for the patience.

[radeksimko]

Suggested change

	body: 'backend: Fix nil pointer dereference crash during `terraform init -migrate-state` when the destination backend returns a permission error'
	body: 'backend: Fix nil pointer dereference crash during `terraform init` when the destination backend returns an error'

As far as I can tell this is reproducible without the flag and applies to any kind of error.