slink assures me that blobs can use size_t for ->len, and that this

one <= 0 test is an oversight.

include/vrt.h

@@ -178,7 +178,7 @@ struct strands {
 
 struct vrt_blob {
 	unsigned	type;
-	long		len;
+	size_t		len;
 	const void	*blob;
 };
 

lib/libvmod_directors/vmod_shard.c

@@ -571,7 +571,7 @@ shard_param_args(VRT_CTX,
 					 who, p->vcl_name, by_s);
 				return (NULL);
 			}
-			if (key_blob == NULL || key_blob->len <= 0 ||
+			if (key_blob == NULL || key_blob->len == 0 ||
 			    key_blob->blob == NULL) {
 				sharddir_err(ctx, SLT_Error, "%s %s: "
 					     "by=BLOB but no or empty key_blob "