修复自动换源的bug

app/src/main/java/io/legado/app/service/help/ReadBook.kt

@@ -263,9 +263,10 @@ object ReadBook {
     }
 
     private fun download(chapter: BookChapter, resetPageOffset: Boolean) {
-        book?.let { book ->
+        val book = book
-            webBook?.let {
+        val webBook = webBook
-                it.getContent(book, chapter)
+        if (book != null && webBook != null) {
+            webBook.getContent(book, chapter)
                 .onSuccess(Dispatchers.IO) { content ->
                     if (content.isEmpty()) {
                         contentLoadFinish(
@@ -294,7 +295,7 @@ object ReadBook {
                     )
                     removeLoading(chapter.index)
                 }
-            } ?: let {
+        } else if (book != null) {
             contentLoadFinish(
                 book,
                 chapter,
@@ -302,8 +303,9 @@ object ReadBook {
                 resetPageOffset = resetPageOffset
             )
             removeLoading(chapter.index)
+        } else {
+            removeLoading(chapter.index)
         }
-        } ?: removeLoading(chapter.index)
     }
 
     private fun addLoading(index: Int): Boolean {