Ensure report-built-images doesn't fail when no images were built

Signed-off-by: Rémy Coutable <remy@rymai.me>

.gitlab/ci/definitions.yml

@@ -57,6 +57,7 @@
         -t "$CI_REGISTRY_IMAGE:$IMAGE_NAME" \
         -f "Dockerfile.$IMAGE_NAME" \
         .
+    - 'echo "${CI_JOB_URL}: ${IMAGE_NAME}" > "${CI_JOB_ID}-${CI_JOB_NAME_SLUG}-built-image.txt"'
   rules:
     - if: '$CI_PIPELINE_SOURCE == "schedule"'
       when: never

.gitlab/ci/report.yml

@@ -2,8 +2,19 @@ report-built-images:
   image: alpine
   stage: report
   script:
-    - cat *-built-image.txt > all-built-images.txt
+    - |
-    - cat all-built-images.txt
+      set -- "${CI_PROJECT_DIR}"/*-built-image.txt
+
+      while [ "$#" -gt 0 ] && [ ! -f "$1" ]; do
+        shift
+      done
+
+      if [ -f "$1" ]; then
+        cat *-built-image.txt > all-built-images.txt
+        cat all-built-images.txt
+      else
+        echo "No images built";
+      fi
   artifacts:
     paths: ["all-built-images.txt"]
     expire_in: 90d