fix: allow preprocess plugin to run twice

[bluwy]

The internal preprocess plugin deletes the transform hook if no preprocessors were configured in configResolved, but this causes an error if configResolved were to be executed again, e.g. the plugin is reused in a multiple build setup.

I found this issue in my publint vitepress setup (which is a weird setup, but maybe some frameworks also reuse plugins):

  vitepress v2.0.0-alpha.12

✗ building client + server bundles...
build error:
Cannot set properties of undefined (setting 'filter')
TypeError: Cannot set properties of undefined (setting 'filter')
    at BasicMinimalPluginContext.configResolved (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/@[email protected][email protected][email protected]_@[email protected][email protected]_/node_modules/@sveltejs/vite-plugin-svelte/src/plugins/preprocess.js:35:28)
    at file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected]/node_modules/vite/dist/node/chunks/dep-Bj7gA1-0.js:36285:87
    at Array.map (<anonymous>)
    at resolveConfig (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected]/node_modules/vite/dist/node/chunks/dep-Bj7gA1-0.js:36285:68)
    at async createBuilder (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected]/node_modules/vite/dist/node/chunks/dep-Bj7gA1-0.js:34478:19)
    at async build$1 (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected]/node_modules/vite/dist/node/chunks/dep-Bj7gA1-0.js:34032:18)
    at async file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/vitepress/dist/node/chunk-3d7P_gGE.js:42551:20
    at async task (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/vitepress/dist/node/chunk-3d7P_gGE.js:41802:5)
    at async bundle (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/vitepress/dist/node/chunk-3d7P_gGE.js:42549:3)
    at async build (file:///Users/bjorn/Work/oss/publint/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/vitepress/dist/node/chunk-3d7P_gGE.js:46805:59)