c/main: Normalize destroy pattern for comp_renderer.

src/xrt/compositor/main/comp_compositor.c

@@ -552,10 +552,7 @@ compositor_destroy(struct xrt_compositor *xc)
 	// Make sure we don't have anything to destroy.
 	comp_compositor_garbage_collect(c);
 
-	if (c->r) {
-		comp_renderer_destroy(c->r);
-		c->r = NULL;
-	}
+	comp_renderer_destroy(&c->r);
 
 	comp_resources_close(c, &c->nr);
 

src/xrt/compositor/main/comp_renderer.c

@@ -120,10 +120,18 @@ comp_renderer_create(struct comp_compositor *c)
 }
 
 void
-comp_renderer_destroy(struct comp_renderer *r)
+comp_renderer_destroy(struct comp_renderer **ptr_r)
 {
+	if (ptr_r == NULL) {
+		return;
+	}
+	struct comp_renderer *r = *ptr_r;
+	if (r == NULL) {
+		return;
+	}
 	renderer_destroy(r);
 	free(r);
+	*ptr_r = NULL;
 }
 
 /*

src/xrt/compositor/main/comp_renderer.h

@@ -38,11 +38,13 @@ comp_renderer_create(struct comp_compositor *c);
 /*!
  * Clean up and free the renderer.
  *
+ * Does null checking and sets to null after freeing.
+ *
  * @public @memberof comp_renderer
  * @ingroup comp_main
  */
 void
-comp_renderer_destroy(struct comp_renderer *r);
+comp_renderer_destroy(struct comp_renderer **ptr_r);
 
 /*!
  * Render frame.