buffer: do not leak memory if buffer is too big

A recent pull request changed this method to throw when the buffer was
too big, but this meant that the `free` finalizer would never get
called, leading to a memory leak.

A previous version of this diff included a test provoking this behavior
with `v8.serialize`, but it unfortunately kept triggering the OOM
killer, so it was removed.

Refs: nodejs#40243

PR-URL: nodejs#43938
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/node_buffer.cc

@@ -497,6 +497,7 @@ MaybeLocal<Object> New(Environment* env,
     if (length > kMaxLength) {
       Isolate* isolate(env->isolate());
       isolate->ThrowException(ERR_BUFFER_TOO_LARGE(isolate));
+      free(data);
       return Local<Object>();
     }
   }