fix(platform-fastify): fix streamable file processing

Author: kamilmysliwiec

packages/platform-fastify/adapters/fastify-adapter.ts

@@ -280,14 +280,14 @@ export class FastifyAdapter<
       fastifyReply.status(statusCode);
     }
     if (body instanceof StreamableFile) {
-      body = body.getStream();
       const streamHeaders = body.getHeaders();
       if (fastifyReply.getHeader('Content-Type') === undefined) {
         fastifyReply.header('Content-Type', streamHeaders.type);
       }
       if (fastifyReply.getHeader('Content-Disposition') === undefined) {
         fastifyReply.header('Content-Disposition', streamHeaders.disposition);
       }
+      body = body.getStream();
     }
     return fastifyReply.send(body);
   }