MINOR: server: diag for 0 weight server

Output a diagnostic report if a server has been configured with a null
weight.
diff --git a/src/server.c b/src/server.c
index dde78e8..9043a77 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2702,6 +2702,10 @@
 	if (parse_flags & SRV_PARSE_TEMPLATE)
 		_srv_parse_tmpl_init(newsrv, curproxy);
 
+	HA_DIAG_WARNING_COND(!newsrv->uweight,
+	                     "parsing [%s:%d] : 'server %s' : configured with weight of 0 will never be selected by load balancing algorithms\n",
+	                     file, linenum, newsrv->id);
+
 	return 0;
 
  out: