fix: coin change with empty box

packages/server/lib/coin-change.js

@@ -9,12 +9,12 @@
  */
 const prepare_denominations = denominations =>
   JSON.parse(JSON.stringify(denominations))
-    .sort(([d1], [d2]) => d2 - d1)
+    .filter(([, count]) => count > 0)
+    .sort(([d1], [d2]) => d1 - d2)
     .reduce(
       ([csum, denoms], [denom, count]) => {
         csum += denom * count
-        denoms.push({ denom, count, csum })
-        return [csum, denoms]
+        return [csum, [{ denom, count, csum }].concat(denoms)]
       },
       [0, []],
     )[1] /* ([csum, denoms]) => denoms */