Coverage build failing due to empty corpus.

We are implementing fuzzing for [envoy/gateway](https://github.com/envoyproxy/gateway) and are encountering a **failed coverage build** in OSS-Fuzz. In step 5, one of our fuzzer's corpus _(FuzzGatewayClassToXDS.zip)_ is empty, which appears to be causing the coverage build to fail.

However, the fuzzer seems to be running—as indicated by the fuzzing build logs—so we’re unsure why the generated corpus is empty in OSS-Fuzz.

**Part of coverage build logs:**
```
Step #5: Already have image (with digest): gcr.io/oss-fuzz-base/base-runner
Step #5: warning [/corpus/FuzzGatewayClassToXDS.zip]: zipfile is empty
Step #5: Failed to unpack the corpus for FuzzGatewayClassToXDS. This usually means that corpus backup for a particular fuzz target does not exist. If a fuzz target was added in the last 24 hours, please wait one more day. Otherwise, something is wrong with the fuzz target or the infrastructure, and corpus pruning task does not finish successfully.
```
**Full logs:** https://oss-fuzz-build-logs.storage.googleapis.com/log-c66bc443-1cd4-4255-8d0a-cc0ec9a1fd87.txt

Start with the linked full coverage-build log and the warning for FuzzGatewayClassToXDS.zip. Trace whether the empty corpus comes from the fuzzer or OSS-Fuzz corpus pruning and coverage-build infrastructure; done means the corpus is populated or the underlying failure is identified and reproducible.

Written by the indexing model from the issue text.