Fix pushbutton under water causing Tux to move to standing action

src/object/pushbutton.cpp

@@ -113,7 +113,10 @@ PushButton::collision(MovingObject& other, const CollisionHit& hit)
       if (hit.top)
       {
         player->get_physic().set_velocity_y(0);
-        player->set_on_ground(true);
+        if(!player->is_swimming())
+        {
+          player->set_on_ground(true);
+        }
       }
     }
 	}