net: eliminate bounds checks in hasUpperCase

[jub0bs]

Function hasUpperCase accesses its parameter's bytes while iterating
over its runes. This approach muddles intent and causes an unnecessary
bounds check.

This CL makes hasUpperCase iterate over its parameter's bytes instead.

Updates #76354

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Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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Message from jub0bs:

Patch Set 2:

(1 comment)

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Message from jub0bs:

Patch Set 2:

(1 comment)

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Message from Ian Lance Taylor:

Patch Set 2:

(1 comment)

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Message from jub0bs:

Patch Set 2:

(1 comment)

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Message from Olivier Mengué:

Patch Set 3: Code-Review+1

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