Clarify comment, add assert + comment

bin/varnishd/cache/cache_fetch.c

@@ -572,9 +572,8 @@ FetchBody(struct worker *wrk, struct object *obj)
 	AZ(bo->vgz_rx);
 
 	/*
-	 * It is OK for ->end to just leave the last storage segment
-	 * sitting on wrk->storage, we will always call vfp_nop_end()
-	 * to get it trimmed or thrown out if empty.
+	 * We always call vfp_nop_end() to ditch or trim the last storage
+	 * segment, to avoid having to replicate that code in all vfp's.
 	 */
 	AZ(vfp_nop_end(bo));
 

bin/varnishd/storage/stevedore.c

@@ -177,6 +177,8 @@ stv_alloc(struct busyobj *bo, size_t size)
 	if (size > cache_param->fetch_maxchunksize)
 		size = cache_param->fetch_maxchunksize;
 
+	assert(size <= UINT_MAX);	/* field limit in struct storage */
+
 	for (;;) {
 		/* try to allocate from it */
 		AN(stv->alloc);