[Fix,Roofline] Handle zero length features in roofline

[tkonolige]

These features may occur for extern ops.

[tvm-bot]

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• No users to tag found in teams: fix, roofline _{See #10317 for details}
• Built docs for commit 1e4f339 can be found here.

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[tvm-bot]

Thanks for contributing to TVM! Please refer to the contributing guidelines https://tvm.apache.org/docs/contribute/ for useful information and tips. Please request code reviews from Reviewers by @-ing them in a comment.

• No users to tag found in teams: fix, roofline _{See #10317 for details}

_{Generated by tvm-bot}