Fix latest run check in toolchain upload script

Author: MaxDesiatov

utils/webassembly/distribute-latest-toolchain.sh

@@ -13,6 +13,12 @@ github() {
 
 latest_run=$(github "${gh_api}/repos/${repository}/actions/workflows/${workflow_name}/runs?head_branch=${branch}&status=completed&conclusion=success" \
   | jq ".workflow_runs | map(select(.head_branch == \"$branch\")) | sort_by(.run_number) | last")
+
+if [ -z "$latest_run" ] || [ "$latest_run" == "null" ]; then
+  echo "No successful runs available"
+  exit 0
+fi
+
 artifacts_url=$(echo $latest_run | jq .artifacts_url --raw-output)
 head_sha=$(echo $latest_run | jq .head_sha --raw-output)