fix(mixedModuleGraph): handle undefined id in getModulesByFile

[bluwy]

Description

Handle undefined id in getModulesByFile. I tested it manually with Astro to verify that it fixes its e2e tests, but I've not added test (withastro/astro#11979) 😬

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[patak-dev]

I still don't understand why we have modules without an id 🤔
Let's merge this though to unblock testing other things in Astro.

[sapphi-red]

This seems to be the reason.

vite/packages/vite/src/node/server/moduleGraph.ts

Lines 388 to 391 in b513836

	// some deps, like a css file referenced via @import, don't have its own
	// url because they are inlined into the main css import. But they still
	// need to be represented in the module graph so that they can trigger
	// hmr in the importing css file.