Fix saving signed revisions of a signature

We don't need a QDataStream to assign a QByteArray to a QByteArray, and
it was adding some noise at the beginning which is clearly not what we
want

core/document.cpp

@@ -4921,9 +4921,7 @@ QByteArray Document::requestSignedRevisionData(const Okular::SignatureInfo &info
 
     const QList<qint64> byteRange = info.signedRangeBounds();
     f.seek(byteRange.first());
-    QByteArray data;
-    QDataStream stream(&data, QIODevice::WriteOnly);
-    stream << f.read(byteRange.last() - byteRange.first());
+    QByteArray data = f.read(byteRange.last() - byteRange.first());
     f.close();
 
     return data;