roll: pigweed, pw_toolchain: pw_transfer: Don't assert on resource status responder

An RPC call can close for various reasons, such as a client requesting a
cancel or their channel shutting down. Code should never assert on RPC
call objects being open. This updates the GetResourceStatus RPC callback
to simply log an error if its responder object is no longer active.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/219037
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>

https://pigweed.googlesource.com/pigweed/pigweed
pigweed, pw_toolchain Rolled-Commits: 62da50a4f4cb9b5..4200619994a4a8d
Roller-URL: https://ci.chromium.org/b/8743832777022223281
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: If4a0c5fc0601386a5b0522bf242ce657b1c2baac
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/showcase/rp2/+/219043
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>