fix JSON.parse for summerize (#445)

* fix JSON.parse for summerize

When serving with TGI, summerize calls this function and it errors with `SyntaxError: Unexpected token d in JSON at position 0`

This PR fixes the problem and keeps existing behaviour.

* fix types

---------

Co-authored-by: Nathan Sarrazin <sarrazin.nathan@gmail.com>

src/lib/server/generateFromDefaultEndpoint.ts

@@ -87,7 +87,12 @@ export async function generateFromDefaultEndpoint(
 	// Close the reader when done
 	reader.releaseLock();
 
-	const results = await JSON.parse(result);
+	let results;
+	if (result.startsWith("data:")) {
+		results = [JSON.parse(result.split("data:")?.pop() ?? "")];
+	} else {
+		results = JSON.parse(result);
+	}
 
 	let generated_text = trimSuffix(
 		trimPrefix(trimPrefix(results[0].generated_text, "<|startoftext|>"), prompt),