fix project reading error introduced with global renaming "OffSpecInstrument"...

fix project reading error introduced with global renaming "OffSpecInstrument" -> "OffSpecularInstrument"

GUI/Models/ItemCatalog.cpp

@@ -79,6 +79,9 @@ ItemCatalog::ItemCatalog()
     add("InterferenceRadialParaCrystal", create_new<InterferenceFunctionRadialParaCrystalItem>);
     add("GISASInstrument", create_new<GISASInstrumentItem>);
     add("OffSpecularInstrument", create_new<OffSpecularInstrumentItem>);
+    // the following line is necessary for loading BornAgain projects which have been created before
+    // global renaming to "OffSpecularInstrument"
+    add("OffSpecInstrument", create_new<OffSpecularInstrumentItem>);
     add("SpecularInstrument", create_new<SpecularInstrumentItem>);
     addItem<GISASBeamItem>();
     addItem<SpecularBeamItem>();