Don't display error stack when not needed, and if needed check it exist

before trying to display it.

src/batch.ts

@@ -66,14 +66,14 @@ export default function(args: string[], done: (err?: Error) => void)
         {
           if (tasksArr[i].retry <= 0)
           {
-            console.error(err.stack || err);
+            console.error(err);
             log.error('Cannot get episodes from "' + tasksArr[i].address + '", please rerun later');
           }
           else
           {
             if (config.verbose)
             {
-              console.error(err.stack || err);
+              console.error(err);
             }
             log.warn('Retrying to fetch episodes ' + tasksArr[i].retry + ' / ' + config.retry);
             tasksArr[i].retry -= 1;

src/cli.ts

@@ -26,7 +26,14 @@ batch(process.argv, (err: any) =>
 {
   if (err)
   {
-    console.error(err.stack || err);
+    if (err.stack)
+    {
+      console.error(err.stack || err);
+    }
+    else
+    {
+      console.error(err);
+    }
     process.exit(-1);
   }
   console.info('Done!');