fix: import.meta.env and process.env undefined variable replacement (fix #8663)

[julienv3]

Description

Fixes Vite using the replacement for "import.meta.env" instead of the replacement for "import.meta.env." when replacing an undefined environment variable (and any other "."-ending replacement never being used)
fix #8663

Additional context

Code:
import.meta.env.UNDEFINED
Expected replacement:
({}).UNDEFINED
Actual replacement:
{"BASE_URL":"/","MODE":"production","DEV":false,"PROD":true}.UNDEFINED

Note that the above is inlining the full list of known env variables but also creating invalid JavaScript in some scenarios.
Issue originally reported at #8663
Additional broken build repro:
https://stackblitz.com/edit/vitejs-vite-bthpb6?file=main.js&terminal=build

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

Thanks for the fix!