Fix uninitialized variable

code/renderergl2/tr_backend.c

@@ -423,7 +423,7 @@ RB_RenderDrawSurfList
 ==================
 */
 void RB_RenderDrawSurfList( drawSurf_t *drawSurfs, int numDrawSurfs ) {
-	shader_t		*shader, *oldShader;
+	shader_t		*shader = NULL, *oldShader;
 	int				fogNum, oldFogNum;
 	int				entityNum, oldEntityNum;
 	int				dlighted, oldDlighted;