Do not access invalid memory when BrowserActionResult is empty.

This fixes a crash in the Experimental Actor API, when the
BrowserActionResult is empty (which can happen because 0 is currently
the error status), it should not try to serialize to an empty data
buffer.

Low-Coverage-Reason: EXPERIMENTAL_CODE This code won't be released to real users and is hard to test compared to the benefits we'd gain from testing this change.
Bug: 413473015, 414446576
Change-Id: Ic0ed55d6c9ce51fa75e23e321ab316b99910ca4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6492390
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Devlin Cronin <rdevlin.cronin@chromium.org>
Auto-Submit: Simon Pelchat <spelchat@chromium.org>
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1452985}