Fix clearing piece transformation.

Mirror state must be cleared as well.

src/app/puzzle/layout/vppiece.cpp

@@ -185,6 +185,8 @@ void VPPiece::ClearTransformations()
     // (0,0) in the sheet coordinate system
     const QPointF offset = MappedDetailBoundingRect().topLeft();
     Translate(-offset.x(), -offset.y());
+
+    SetMirror(false);
 }
 
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