fix a few compiler warnings

libs/ardour/midi_model.cc

@@ -179,6 +179,8 @@ MidiModel::NoteDiffCommand::get_value (const NotePtr note, Property prop)
 	case Length:
 		return Variant(note->length());
 	}
+
+	return Variant ();
 }
 
 Variant::Type
@@ -193,6 +195,8 @@ MidiModel::NoteDiffCommand::value_type(Property prop)
 	case Length:
 		return Variant::BEATS;
 	}
+
+	return Variant::NOTHING;
 }
 
 void

libs/ardour/transform.cc

@@ -62,6 +62,8 @@ Transform::Value::eval(const Context& ctx) const
 	case RANDOM:
 		return Variant(g_random_double());
 	}
+
+	return Variant ();
 }
 
 void