guided mode altitude slider better maximum

src/FlightDisplay/FlightDisplayViewWidgets.qml

@@ -452,8 +452,8 @@ Item {
             anchors.left:       parent.left
             anchors.right:      parent.right
             orientation:        Qt.Vertical
-            minimumValue:       QGroundControl.metersToAppSettingsDistanceUnits(2)
-            maximumValue:       QGroundControl.metersToAppSettingsDistanceUnits((_activeVehicle && _activeVehicle.flying) ? 100 : 10)
+            minimumValue:       QGroundControl.metersToAppSettingsDistanceUnits(0)
+            maximumValue:       QGroundControl.metersToAppSettingsDistanceUnits((_activeVehicle && _activeVehicle.flying) ? Math.round((_activeVehicle.altitudeRelative.value + 100) / 100) * 100 : 10)
         }
     }
 }