fix: 修复当不指定下载线程时，下载线程为NaN的bug

Author: ZeroWolf233

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "openmcim",
-  "version": "1.1.4",
+  "version": "1.1.5",
   "description": "mcim@home",
   "bin": "dist/openmcim.js",
   "private": true,

package.json

@@ -187,7 +187,7 @@ export class Cluster {
       notTTYSchedule: ms('10s'),
     })
     const totalBar = multibar.create(missingFiles.length, 0, {filename: '总文件数'})
-    const parallel = Number(process.env.THREADS) ?? syncConfig.concurrency
+    const parallel = Number(process.env.THREADS) || syncConfig.concurrency
     logger.info(`您当前的下载线程: ${parallel} `)
     let hasError = false
     await pMap(