BUG/MINOR: peers: crash on reload without local peer.

When we configure a "peers" section without local peer, this makes haproxy
old process crash on reload.

Such a configuration file allows to reproduce this issue:

  global
    stats socket /tmp/sock1 mode 666 level admin
    stats timeout 10s

  peers peers
    peer localhost 127.0.0.1:1024

This bug was introduced by this commit:
  "MINOR: cfgparse: Make "peer" lines be parsed as "server" lines"

This commit introduced a new condition to detect a "peers" section without
local peer. This is a "peers" section with a frontend struct which has no ->id
initialized member. Such a "peers" section must be removed.

This patch adds this new condition to remove such peers sections without local
peer as this was always done before.

Must be backported to 2.0.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 6cbcac4..05a64a8 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -3903,7 +3903,7 @@
 					stop_proxy(curpeers->peers_fe);
 				curpeers->peers_fe = NULL;
 			}
-			else if (!curpeers->peers_fe) {
+			else if (!curpeers->peers_fe || !curpeers->peers_fe->id) {
 				ha_warning("Removing incomplete section 'peers %s' (no peer named '%s').\n",
 					   curpeers->id, localpeer);
 			}