Test error handling for an illegal file name.

src/tests/get.vtc

@@ -91,3 +91,12 @@ varnish v1 -errvcl {not a regular file} {
 		new rdr = file.reader("${tmpdir}");
 	}
 }
+
+varnish v1 -errvcl {vmod file failure: new rdr: name is empty} {
+	import ${vmod_file};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new rdr = file.reader("");
+	}
+}