Fix overwriting feeds.json with an incomplete load of it

PR #19444.
Closes #19439.

---------

Co-authored-by: Vladimir Golovnev <glassez@yandex.ru>

src/base/rss/rss_session.cpp

@@ -271,6 +271,7 @@ void Session::load()
         if (readResult.error().status == Utils::IO::ReadError::NotExist)
         {
             loadLegacy();
+            store(); // convert to new format
             return;
         }
 
@@ -294,10 +295,11 @@ void Session::load()
         return;
     }
 
-    loadFolder(jsonDoc.object(), rootFolder());
+    if (loadFolder(jsonDoc.object(), rootFolder()))
+        store(); // convert to updated format
 }
 
-void Session::loadFolder(const QJsonObject &jsonObj, Folder *folder)
+bool Session::loadFolder(const QJsonObject &jsonObj, Folder *folder)
 {
     bool updated = false;
     for (const QString &key : asConst(jsonObj.keys()))
@@ -353,7 +355,8 @@ void Session::loadFolder(const QJsonObject &jsonObj, Folder *folder)
             }
             else
             {
-                loadFolder(valObj, addSubfolder(key, folder));
+                if (loadFolder(valObj, addSubfolder(key, folder)))
+                    updated = true;
             }
         }
         else
@@ -363,8 +366,7 @@ void Session::loadFolder(const QJsonObject &jsonObj, Folder *folder)
         }
     }
 
-    if (updated)
-        store(); // convert to updated format
+    return updated;
 }
 
 void Session::loadLegacy()
@@ -394,8 +396,6 @@ void Session::loadLegacy()
         addFeed(feedUrl, feedPath);
         ++i;
     }
-
-    store(); // convert to new format
 }
 
 void Session::store()

src/base/rss/rss_session.h

@@ -149,7 +149,7 @@ namespace RSS
     private:
         QUuid generateUID() const;
         void load();
-        void loadFolder(const QJsonObject &jsonObj, Folder *folder);
+        bool loadFolder(const QJsonObject &jsonObj, Folder *folder);
         void loadLegacy();
         void store();
         nonstd::expected<Folder *, QString> prepareItemDest(const QString &path);