Adds header safeguards to LOSTexture forgotten in fe21c5e023.

This was SVN commit r25620.

source/graphics/LOSTexture.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2019 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -15,6 +15,9 @@
  * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifndef INCLUDED_LOSTEXTURE
+#define INCLUDED_LOSTEXTURE
+
 #include "lib/ogl.h"
 
 #include "graphics/ShaderTechniquePtr.h"
@@ -103,3 +106,5 @@ private:
 	CMatrix3D m_TextureMatrix;
 	CMatrix3D m_MinimapTextureMatrix;
 };
+
+#endif // INCLUDED_LOSTEXTURE