[FEM] pipeline fix when there is no field

- for the case that pipeline with a field is active, then another pipeline that does not display any field, we cannot just return because the pipeline cannot have the color bar range of the prevision pipeline

src/Mod/Fem/Gui/ViewProviderFemPostObject.cpp

@@ -538,6 +538,9 @@ void ViewProviderFemPostObject::WriteColorData(bool ResetColorBarRange) {
         m_material->transparency.setValue(0.);
         m_materialBinding->value = SoMaterialBinding::OVERALL;
         m_materialBinding->touch();
+        // since there is no field, set the range to the default
+        // range as if a new object is created
+        setRangeOfColorBar(-0.5, 0.5);
         return;
     };