Fix a compiler warning.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@1102 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

code/SceneCombiner.cpp

@@ -967,7 +967,7 @@ void SceneCombiner::CopyScene(aiScene** _dest,const aiScene* src,bool allocate)
 	dest->mFlags = src->mFlags;
 
 	// source private data might be NULL if the scene is user-allocated (i.e. for use with the export API)
-	ScenePriv(dest)->mPPStepsApplied = ScenePriv(src) ? ScenePriv(src)->mPPStepsApplied : NULL;
+	ScenePriv(dest)->mPPStepsApplied = ScenePriv(src) ? ScenePriv(src)->mPPStepsApplied : 0;
 }
 
 // ------------------------------------------------------------------------------------------------