jabber: Fix off-by-one strncpy() error

warning: ‘__builtin_strncpy’ output truncated before terminating nul
copying as many bytes from a string as its length [-Wstringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bo...
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...
xjab_wlist.c: In function ‘xj_wlist_set_aliases’:
xjab_wlist.c:455:34: note: length computed here
  455 |   i = jwl->aliases->proxy->len = strlen(pa);
      |                                  ^~~~~~~~~~

(cherry picked from commit 2d98eef)

modules/jabber/xjab_wlist.c

@@ -470,7 +470,7 @@ int  xj_wlist_set_aliases(xj_wlist jwl, char *als, char *jd, char *pa)
 			strncpy(p0, "sip:", 5);
 			p0 += 4;
 		}
-		strncpy(p0, pa, i);
+		strncpy(p0, pa, i+1);
 #ifdef XJ_EXTRA_DEBUG
 		LM_DBG("outbound proxy=[%.*s]\n",
 			jwl->aliases->proxy->len, jwl->aliases->proxy->s);