Handle missing last release in build workflow

Author: OllyButters

.github/workflows/build_packages_info.yml

@@ -51,7 +51,12 @@ jobs:
             echo "last commit: $gh_last_commit"
 
             # Last release
-            gh_last_release=$(git describe --tags $(git rev-list --tags --max-count=1))
+            {
+              gh_last_release=$(git describe --tags $(git rev-list --tags --max-count=1)) &&
+            } ||
+            {
+              gh_last_release=""
+            }
             echo "last GitHub release: $gh_last_release"
 
             # Tidy up