Fix: qnan detection code. Appearently I fooled myself when I wrote this.

Fix: MDLLoader does not reset texture array properly when textures are substituted by plain colors. This caused crashes in ~aiScene or heap corruption.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@677 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

code/MDLLoader.cpp

@@ -510,6 +510,8 @@ void MDLImporter::SetupMaterialProperties_3DGS_MDL5_Quake1( )
 		if (is_not_qnan(clr.r))	{
 			delete pScene->mTextures[0];
 			delete[] pScene->mTextures;
+
+			pScene->mTextures = NULL;
 			pScene->mNumTextures = 0;
 		}
 		else	{