Failed coverage building for cups-filters

he latest building of coverage sanitizer for cups-filters has failed.

The build logs are as follows:

Finished Step #4
Starting Step #5
Step #5: Already have image (with digest): gcr.io/oss-fuzz-base/base-runner
Step #5: warning [/corpus/fuzzpdf.zip]:  zipfile is empty
Step #5: Failed to unpack the corpus for fuzzpdf. 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.
Step #5: ********************************************************************************
Step #5: Code coverage report generation failed.
Step #5: To reproduce, run:
Step #5: python infra/helper.py build_image cups-filters
Step #5: python infra/helper.py build_fuzzers --sanitizer coverage cups-filters
Step #5: python infra/helper.py coverage cups-filters
Step #5: ********************************************************************************
Finished Step #5
ERROR
ERROR: build step 5 "gcr.io/oss-fuzz-base/base-runner" failed: step exited with non-zero status: 1

The primary issue seems to be the absence of the fuzz corpus files. I suppose this is due to some keyword filtering specific to the coverage sanitizer build process, as builds and tests for address and memory sanitizers have been successful. Investigating...

Start with the reproduction commands in the issue, especially the coverage step for cups-filters, and inspect the fuzzpdf corpus warning in the build logs. Determine why the coverage build cannot unpack the corpus while address and memory builds succeed. Done means the coverage report completes without the empty-corpus failure.