utils: fix plus when resulting high part is 0

dist/utils.js

@@ -17,6 +17,8 @@ const bigNumPlus = (num1, num2) => {
     else {
         [high, low] = [high + Math.trunc(low / Math.pow(10, 15)), low % Math.pow(10, 15)];
     }
+    if (high === 0)
+        return low.toString();
     return `${high}${Math.abs(low).toString().padStart(15, '0')}`;
 };
 const bigNumCompare = (num1, num2) => Math.sign(Number(bigNumPlus(num1, num2.replace(/^([+-]?)(\d+)/, (_, $1, $2) => `${$1 === '-' ? '' : '-'}${$2}`))));

src/utils.ts

@@ -20,6 +20,7 @@ const bigNumPlus = (num1: string, num2: string) => {
   } else {
     [high, low] = [high + Math.trunc(low / 10 ** 15), low % 10 ** 15];
   }
+  if (high === 0) return low.toString();
   return `${high}${Math.abs(low).toString().padStart(15, '0')}`;
 };