[fix] externalize middlewares.js when not using entryPoint

[Conduitry]

#2482 introduced a silly regression where normal builds not using entryPoint (where middlewares.js is (internally) imported from its normal location at .svelte-kit/node/middlewares.js) stopped having middlewares.js external. We need to check both possible paths.

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Latest commit: 7a529d0

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@sveltejs/adapter-node	Patch

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