fix(esbuild): check server before reload tsconfig

[bluwy]

Description

Astro currently watches and reload tsconfig changes itself. When a tsconfig.json is updated, it closes the Vite dev server immediately, which synchronously invokes:

vite/packages/vite/src/node/plugins/esbuild.ts

Line 253 in 7112d7a

server = null as any

But since Vite's watcher is still tearing down at:

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

Line 417 in 7112d7a

watcher.close(),

It could trigger Vite's tsconfig reload watch handler that now relies on server that is null:

vite/packages/vite/src/node/plugins/esbuild.ts

Lines 487 to 498 in a65d31b

	function reloadOnTsconfigChange(changedFile: string) {
	// any tsconfig.json that's added in the workspace could be closer to a code file than a previously cached one
	// any json file in the tsconfig cache could have been used to compile ts
	if (
	path.basename(changedFile) === 'tsconfig.json' ||
	(changedFile.endsWith('.json') &&
	tsconfckParseOptions?.cache?.has(changedFile))
	) {
	server.config.logger.info(
	`changed tsconfig file detected: ${changedFile} - Clearing cache and forcing full-reload to ensure TypeScript is compiled with updated config values.`,
	{ clear: server.config.clearScreen, timestamp: true },
	)

This PR adds a null check to the handler to cover this case.

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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