trapme: No error message when "empty" UPSTREAM_JOB_NUMBER specified

[sxa]

Spotted on https://ci.adoptium.net/job/Test_openjdk21_hs_extended.openjdk_riscv64_linux/32/console

That job seems to have failed because it specified an UPSTREAM_JOB_NUMBER which no longer had any associated artifacts, but that is not obvious in the log:

12:44:17  Timeout set to expire in 1 hr 0 min
[Pipeline] {
[Pipeline] dir
12:44:17  Running in /home/jenkins/workspace/Test_openjdk21_hs_extended.openjdk_riscv64_linux/jdkbinary
[Pipeline] {
[Pipeline] copyArtifacts
[Pipeline] }
[Pipeline] // dir
[Pipeline] }
[Pipeline] // timeout
[Pipeline] }
[Pipeline] // stage
[Pipeline] echo
12:44:17  PROCESSCATCH: Terminating any hung/left over test processes:
[Pipeline] sh
12:44:18  + aqa-tests/terminateTestProcesses.sh jenkins
12:44:18  Unix type machine..
12:44:18  Running on a Linux host
12:44:18  Woohoo - no rogue processes detected!
[Pipeline] cleanWs
12:44:18  [WS-CLEANUP] Deleting project workspace...

We should spot this situation and give a suitable error message to make this scenario easier to identify and debug so as not to spend too much time trying to diagnose it.

[llxia]

In the console output, it has the error message

07:44:20  Exception: hudson.AbortException: Failed to copy artifacts from build-scripts/jobs/evaluation/jobs/jdk21u/jdk21u-evaluation-linux-riscv64-temurin with filter: **/*.tar.gz,**/*.tgz,**/*.zip,**/*.jar,**/*.Z,**/*sbom*.json