fix: update key handling in StorageR2Adapter to conditionally prepend keyPrefix

- Modified getKey method to prepend keyPrefix only if it is not empty, ensuring correct key formatting.

app/src/adapter/cloudflare/storage/StorageR2Adapter.ts

@@ -177,8 +177,11 @@ export class StorageR2Adapter extends StorageAdapter {
    }
 
    protected getKey(key: string) {
+      if (this.keyPrefix.length > 0) {
          return `${this.keyPrefix}/${key}`.replace(/^\/\//, "/");
       }
+      return key;
+   }
 
    toJSON(secrets?: boolean) {
       return {