优化

app/src/main/java/io/legado/app/model/CacheBook.kt

@@ -89,10 +89,12 @@ object CacheBook {
     }
 
     fun stop(context: Context) {
+        if (CacheBookService.isRun) {
             context.startService<CacheBookService> {
                 action = IntentAction.stop
             }
         }
+    }
 
     fun clear() {
         successDownloadSet.clear()