serializer: ensure backwards compatibility

app/timeline/timelinemarker.cpp

@@ -164,6 +164,8 @@ bool TimelineMarker::load(QXmlStreamReader *reader)
 
   // This element has no inner text, so just skip it
   reader->skipCurrentElement();
+
+  return true;
 }
 
 void TimelineMarker::save(QXmlStreamWriter *writer) const

app/timeline/timelineworkarea.cpp

@@ -66,6 +66,7 @@ bool TimelineWorkArea::load(QXmlStreamReader *reader)
       version = attr.value().toUInt();
     }
   }
+  Q_UNUSED(version)
 
   while (XMLReadNextStartElement(reader)) {
     if (reader->name() == QStringLiteral("enabled")) {