Arm backend: Fix for security bug reported by Metis, CWE-125

[wwwind]

The security bug is reported by Metis:
"Table decoder pointers are derived from header-provided offsets before the header is validated, so malformed VGF offsets can point outside the vgf_data buffer."
This is the fix.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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❌ 1 New Failure, 5 Pending

As of commit 369dbac with merge base 5e21c13 ():

NEW FAILURE - The following job has failed:

• Cadence Build & Test / Resolve CI docker image / resolve (gh)
  ##[error]Refusing to check out fork pull request code from a 'pull_request_target' workflow. This workflow runs with the base repository's GITHUB_TOKEN, secrets, default-branch cache scope, and runner access. Fetching and executing a fork's code in that trusted context commonly leads to "pwn request" vulnerabilities. To opt in, review the risks at https://gh.io/securely-using-pull_request_target and set 'allow-unsafe-pr-checkout: true' on the actions/checkout step.

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