Avoid allocating large memory when loading a .torrent file

`QIODevice::read(qint64 maxSize)` will allocate full `maxSize` of memory no matter
what the real file size was, this caused users to experience out-of-memory
exception on 32-bit qbt.
Also handle the OOM execption if it still fails.

Closes #9064, #9075, #9130, #9239, #9246, #9279.

src/base/bittorrent/torrentinfo.cpp

@@ -112,10 +112,18 @@ TorrentInfo TorrentInfo::loadFromFile(const QString &path, QString *error) noexc
         return TorrentInfo();
     }
 
-    const QByteArray data = file.read(fileSizeLimit);
+    QByteArray data;
+    try {
+        data = file.readAll();
+    }
+    catch (const std::bad_alloc &e) {
+        if (error)
+            *error = tr("Torrent file read error: %1").arg(e.what());
+        return TorrentInfo();
+    }
     if (data.size() != file.size()) {
         if (error)
-            *error = tr("Torrent file read error");
+            *error = tr("Torrent file read error: size mismatch");
         return TorrentInfo();
     }