SpectrumViewer: fix backward compatibility with silx < 2.0

src/est/gui/XasObjectViewer.py

@@ -436,6 +436,9 @@ class SpectrumViewer(qt.QMainWindow):
                             kwargs["baseline"] = (res.baseline,)
 
                         curve = self._plotWidget.addCurve(**kwargs)
+                        if isinstance(curve, str):
+                            # silx < 2.0
+                            curve = self._plotWidget.getCurve(curve)
                         curve.setAlpha(res.alpha)
                     elif isinstance(res, _XMarkerOperation):
                         if res.x is None or res.x is numpy.nan: