[roll third_party/pigweed] pw_log_rpc: Release payload buffer when unused

The RpcLogDrain::server_writer_ requests a buffer with PayloadBuffer().
If it is not used, say because the drain caught up with the multisink,
and no logs were written, then release the buffer. Otherwise, the
server writer will be in an unsafe state with an unreleased buffer,
which can fail asserts when the server writer is overwritten.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/71900

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 6ea8f21c7b608ab..4a613e5a87149de
Roller-URL: https://ci.chromium.org/b/8828482568052573809
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8828482568052573809
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib0991dbe157983c88aa98635a2835d2eb63c3979
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/72663
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 6ea8f21..4a613e5 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6ea8f21c7b608abc23f06fe7b55d7529d04c1842
+Subproject commit 4a613e5a87149de352fcb5fe7f6ba5e5a9c161e6