[jinja] Fix failing lint (#1860)

Weird, CI didn't pick up this lint error in
#1859.

PR
([success](https://github.com/huggingface/huggingface.js/actions/runs/19744569408/job/56576090622))

<img width="887" height="696" alt="image"
src="https://github.com/user-attachments/assets/b889135e-6977-4300-8c4e-dc2f9b16b374"
/>

Main
([failure](https://github.com/huggingface/huggingface.js/actions/runs/19744642524/job/56576326408))

<img width="946" height="778" alt="image"
src="https://github.com/user-attachments/assets/8470e6b4-d3d2-46ec-bb23-48d9812e2ebd"
/>


cc @coyotte508 probably something to look into

Author: xenova

packages/jinja/src/lexer.ts

@@ -180,9 +180,8 @@ export function tokenize(source: string, options: PreprocessOptions = {}): Token
 	};
 
 	const stripTrailingWhitespace = () => {
-		if (tokens.length === 0) return;
-		const lastToken = tokens.at(-1)!;
-		if (lastToken.type === TOKEN_TYPES.Text) {
+		const lastToken = tokens.at(-1);
+		if (lastToken && lastToken.type === TOKEN_TYPES.Text) {
 			lastToken.value = lastToken.value.trimEnd();
 			if (lastToken.value === "") {
 				tokens.pop(); // Remove empty text token