Bugfix: completed downloads are removed

The commit "Moved download deregistration to ContentManager" introduced
a bug - completed downloads were not properly deregistered.

Note that a simpler fix by adding a single `m_downloads.remove(bookId);`
line in `ContentManager::downloadCompleted()` didn't work (which means
that that function is not always called upon download completion). I am
not going to investigate that issue now, hoping that it will be
automatically resolved once the redesign of download management is
finished.

src/contentmanager.cpp

@@ -486,7 +486,9 @@ void ContentManager::updateDownload(QString bookId)
     if ( downloadState && !downloadState->paused ) {
         // This calls ContentManager::updateDownloadInfos() in a convoluted way
         // and also has some other side-effects
-        managerModel->updateDownload(bookId);
+        if ( ! managerModel->updateDownload(bookId) ) {
+            m_downloads.remove(bookId);
+        }
     }
 }
 

src/contentmanagermodel.cpp

@@ -245,12 +245,12 @@ void ContentManagerModel::updateImage(QString bookId, QString url, QByteArray im
     emit dataChanged(index, index);
 }
 
-void ContentManagerModel::updateDownload(QString bookId)
+bool ContentManagerModel::updateDownload(QString bookId)
 {
     const auto download = m_downloads.value(bookId);
 
     if ( ! download )
-        return;
+        return true;
 
     const auto downloadInfos = KiwixApp::instance()->getContentManager()->updateDownloadInfos(bookId, {"status", "completedLength", "totalLength", "downloadSpeed"});
     const bool downloadStillValid = download->update(downloadInfos);
@@ -269,8 +269,10 @@ void ContentManagerModel::updateDownload(QString bookId)
         const QModelIndex newIndex = this->index(row, 5);
         emit dataChanged(newIndex, newIndex);
     }
+    return downloadStillValid;
 }
 
+
 void ContentManagerModel::pauseDownload(QModelIndex index)
 {
     emit dataChanged(index, index);

src/contentmanagermodel.h

@@ -50,7 +50,7 @@ public slots:
     void pauseDownload(QModelIndex index);
     void resumeDownload(QModelIndex index);
     void removeDownload(QString bookId);
-    void updateDownload(QString bookId);
+    bool updateDownload(QString bookId);
 
 protected: // functions
     bool canFetchMore(const QModelIndex &parent) const override;