[master] c9765cf58 polish assertions

[Nils Goroll]

commit c9765cf5865568107356e8474d1fa265b5b7b83d
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed May 13 17:42:46 2020 +0200

    polish assertions
    
    See comments in #3311, but done slightly differently

diff --git a/bin/varnishd/cache/cache_director.c b/bin/varnishd/cache/cache_director.c
index aebbc7a71..3e6902031 100644
--- a/bin/varnishd/cache/cache_director.c
+++ b/bin/varnishd/cache/cache_director.c
@@ -86,14 +86,18 @@ VRT_VDI_Resolve(VRT_CTX, VCL_BACKEND d)
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 
 	while (d != NULL) {
-		CHECK_OBJ_NOTNULL(d, DIRECTOR_MAGIC);
+		CHECK_OBJ(d, DIRECTOR_MAGIC);
 		AN(d->vdir);
 		if (d->vdir->methods->resolve == NULL)
 			break;
 		d = d->vdir->methods->resolve(ctx, d);
-		CHECK_OBJ_ORNULL(d, DIRECTOR_MAGIC);
 	}
-        return (d);
+	if (d == NULL)
+		return (NULL);
+
+	CHECK_OBJ(d, DIRECTOR_MAGIC);
+	AN(d->vdir);
+	return (d);
 }
 
 static VCL_BACKEND