Properly stop platform.

source/RobotAPI/gui-plugins/PlatformUnitPlugin/PlatformUnitGuiPlugin.cpp

@@ -220,7 +220,7 @@ void PlatformUnitWidget::reportPlatformVelocity(::Ice::Float currentPlatformVelo
 
 void PlatformUnitWidget::stopPlatform()
 {
-    platformUnitProxy->move(0, 0, 0);
+    platformUnitProxy->stopPlatform();
 }
 
 void PlatformUnitWidget::controlPlatformWithKeyboard(int key)