fix: check chunkedCookie is string in server client (#57)

## What kind of change does this PR introduce?

 #26 but with prettier


Full credit to [pfftdammitchris](https://github.com/pfftdammitchris) for
this contribution

src/cookies.ts

@@ -342,7 +342,10 @@ export function createStorageFromOptions(
 
         let decoded = chunkedCookie;
 
-        if (chunkedCookie.startsWith(BASE64_PREFIX)) {
+        if (
+          typeof chunkedCookie === "string" &&
+          chunkedCookie.startsWith(BASE64_PREFIX)
+        ) {
           decoded = stringFromBase64URL(
             chunkedCookie.substring(BASE64_PREFIX.length),
           );