fix: generateCodeFrame infinite loop

[sapphi-red]

Description

fixes #15076
refs #14984

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines, especially the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.

[sapphi-red]

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

Lines 1199 to 1202 in bcc4a61

	? {
	line: warning.endLine,
	column: warning.endColumn - 1, // 1-based
	}

{ endLine: 107, endColumn: 2 } was passed here. So posToNumber(source, { line: 107, column: 1 }) was called.
But the source only has 107 lines. So posToNumber returned a number greater than source.length.