ops: Only build backends that actually exist

production/mempool-start-all

@@ -5,6 +5,7 @@ nvm use v20.12.0
 
 # start all mempool backends that exist
 for site in mainnet mainnet-lightning testnet testnet-lightning testnet4 signet signet-lightning liquid liquidtestnet;do
+    [ ! -e "${HOME}/${site}/backend/" ] && continue
     cd "${HOME}/${site}/backend/" && \
     echo "starting mempool backend: ${site}" && \
     screen -dmS "${site}" sh -c 'while true;do npm run start-production;sleep 1;done'