Fix renderer not clearing some GL extension variables at vid_restart

If renderer is compiled into client (USE_RENDERER_DLOPEN=0) and after
start up set r_allowExtension to 0 and run vid_restart, some extension
were still used.

code/renderergl2/tr_init.c

@@ -1528,6 +1528,11 @@ void RE_Shutdown( qboolean destroyWindow ) {
 		GLimp_Shutdown();
 
 		Com_Memset( &glConfig, 0, sizeof( glConfig ) );
+		Com_Memset( &glRefConfig, 0, sizeof( glRefConfig ) );
+		textureFilterAnisotropic = qfalse;
+		maxAnisotropy = 0;
+		displayAspect = 0.0f;
+
 		Com_Memset( &glState, 0, sizeof( glState ) );
 	}