[roll third_party/pigweed] pw_cpu_exception_cortex_m: Do not report undefined reg values

Updates the string, log, and proto dump utilities to not report
PC, LR, nor PSR register values when they are set to the sentinel
undefined value of -1.

Also cleans up the proto dump function's use of IgnoreError.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/73840

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: d0997578b9635bb..a463f7d569df89a
Roller-URL: https://ci.chromium.org/b/8827915446051932257
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827915446051932257
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I76f8a044aa6820239b16ecb6d0633747c048dd81
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/74021
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 d099757..a463f7d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d0997578b9635bbf8c0bd783cb7ae6b24433ddee
+Subproject commit a463f7d569df89a1e59f62d7d0bd454cba4c4f5c