修复自动换源的bug

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

@@ -263,47 +263,49 @@ object ReadBook {
     }
 
     private fun download(chapter: BookChapter, resetPageOffset: Boolean) {
-        book?.let { book ->
-            webBook?.let {
-                it.getContent(book, chapter)
-                    .onSuccess(Dispatchers.IO) { content ->
-                        if (content.isEmpty()) {
-                            contentLoadFinish(
-                                book,
-                                chapter,
-                                App.INSTANCE.getString(R.string.content_empty),
-                                resetPageOffset = resetPageOffset
-                            )
-                            removeLoading(chapter.index)
-                        } else {
-                            BookHelp.saveContent(book, chapter, content)
-                            contentLoadFinish(
-                                book,
-                                chapter,
-                                content,
-                                resetPageOffset = resetPageOffset
-                            )
-                            removeLoading(chapter.index)
-                        }
-                    }.onError {
+        val book = book
+        val webBook = webBook
+        if (book != null && webBook != null) {
+            webBook.getContent(book, chapter)
+                .onSuccess(Dispatchers.IO) { content ->
+                    if (content.isEmpty()) {
+                        contentLoadFinish(
+                            book,
+                            chapter,
+                            App.INSTANCE.getString(R.string.content_empty),
+                            resetPageOffset = resetPageOffset
+                        )
+                        removeLoading(chapter.index)
+                    } else {
+                        BookHelp.saveContent(book, chapter, content)
                         contentLoadFinish(
                             book,
                             chapter,
-                            it.localizedMessage ?: "未知错误",
+                            content,
                             resetPageOffset = resetPageOffset
                         )
                         removeLoading(chapter.index)
                     }
-            } ?: let {
-                contentLoadFinish(
-                    book,
-                    chapter,
-                    "没有书源",
-                    resetPageOffset = resetPageOffset
-                )
-                removeLoading(chapter.index)
-            }
-        } ?: removeLoading(chapter.index)
+                }.onError {
+                    contentLoadFinish(
+                        book,
+                        chapter,
+                        it.localizedMessage ?: "未知错误",
+                        resetPageOffset = resetPageOffset
+                    )
+                    removeLoading(chapter.index)
+                }
+        } else if (book != null) {
+            contentLoadFinish(
+                book,
+                chapter,
+                "没有书源",
+                resetPageOffset = resetPageOffset
+            )
+            removeLoading(chapter.index)
+        } else {
+            removeLoading(chapter.index)
+        }
     }
 
     private fun addLoading(index: Int): Boolean {