Initialize default varnish instance name in library if no n-argument has been given.

Fixes: #762


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5208 d4fa192b-c00b-0410-8231-f00ffab90ce4

lib/libvarnishapi/vsm.c

@@ -147,6 +147,7 @@ vsm_open(struct VSM_data *vd, int diag)
 
 	CHECK_OBJ_NOTNULL(vd, VSM_MAGIC);
 	AZ(vd->vsm_head);
+	AN(vd->fname);
 
 	vd->vsm_fd = open(vd->fname, O_RDONLY);
 	if (vd->vsm_fd < 0) {
@@ -221,6 +222,8 @@ VSM_Open(struct VSM_data *vd, int diag)
 
 	CHECK_OBJ_NOTNULL(vd, VSM_MAGIC);
 	AZ(vd->vsm_head);
+	if (!vd->n_opt)
+		VSM_n_Arg(vd, "");
 	return (vsm_open(vd, diag));
 }