Fix: Null'ed pointer usage, possible access violation.

This fixes issue #700

Engine/source/T3D/debris.cpp

@@ -659,11 +659,7 @@ void Debris::onRemove()
       }
    }
 
-   if( getSceneManager() )
-      getSceneManager()->removeObjectFromScene(this);
-
-   if( getContainer() )
-      getContainer()->removeObject(this);
+   removeFromScene();
 
    Parent::onRemove();
 }

Engine/source/T3D/fx/explosion.cpp

@@ -964,10 +964,7 @@ void Explosion::onRemove()
       mMainEmitter = NULL;
    }
 
-   if (getSceneManager() != NULL)
-      getSceneManager()->removeObjectFromScene(this);
-   if (getContainer() != NULL)
-      getContainer()->removeObject(this);
+   removeFromScene();
 
    Parent::onRemove();
 }

Engine/source/T3D/fx/splash.cpp

@@ -415,11 +415,7 @@ void Splash::onRemove()
 
    ringList.clear();
 
-   if( getSceneManager() )
-      getSceneManager()->removeObjectFromScene(this);
-
-   if( getContainer() )
-      getContainer()->removeObject(this);
+   removeFromScene();
 
    Parent::onRemove();
 }