Verify that calling .create_stats() on an empty set is not an error.

Even if it is pointless. All stats values are 0 in that case.

src/tests/stats.vtc

@@ -43,6 +43,11 @@ varnish v1 -vcl {
 		n.add("bar");
 		n.add("baz");
 		n.add("quux");
+
+		# Calling .create_stats() on an empty set is
+		# pointless, but not an error.
+		new e = selector.set();
+		e.create_stats();
 	}
 }
 
@@ -56,6 +61,13 @@ varnish v1 -expect SELECTOR.vcl2.p.dmin > 0
 varnish v1 -expect SELECTOR.vcl2.p.dmax > 0
 varnish v1 -expect SELECTOR.vcl2.p.davg > 0
 
+varnish v1 -expect SELECTOR.vcl2.e.elements == 0
+varnish v1 -expect SELECTOR.vcl2.e.nodes == 0
+varnish v1 -expect SELECTOR.vcl2.e.leaves == 0
+varnish v1 -expect SELECTOR.vcl2.e.dmin == 0
+varnish v1 -expect SELECTOR.vcl2.e.dmax == 0
+varnish v1 -expect SELECTOR.vcl2.e.davg == 0
+
 # When vcl1 is set to cold, stats for vcl2.p but not vcl1.s appear.
 varnish v1 -cliok "vcl.state vcl1 cold"
 varnish v1 -vsc SELECTOR.*