Test error handling for an illegal TTL.

And improve the error message a bit.

src/tests/get.vtc

@@ -100,3 +100,12 @@ varnish v1 -errvcl {vmod file failure: new rdr: name is empty} {
 		new rdr = file.reader("");
 	}
 }
+
+varnish v1 -errvcl {vmod file failure: new rdr: ttl -1.000 must be > 0s} {
+	import ${vmod_file};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new rdr = file.reader("foo", ttl=-1s);
+	}
+}

src/vmod_file.c

@@ -208,7 +208,7 @@ vmod_reader__init(VRT_CTX, struct VPFX(file_reader) **rdrp,
 		return;
 	}
 	if (ttl <= 0) {
-		VFAIL(ctx, "new %s: ttl %.03f must be > 0", vcl_name, ttl);
+		VFAIL(ctx, "new %s: ttl %.03f must be > 0s", vcl_name, ttl);
 		return;
 	}