Allows alert access to admins and non-admins w/o allowed networks

Implements #5324

scripts/lua/modules/lua_utils.lua

@@ -768,10 +768,17 @@ function hasAlertsDisabled()
 end
 
 function hasNindexSupport()
+   local auth = require "auth"
+
    if not ntop.isPro() or ntop.isWindows() then
       return false
    end
 
+   -- Don't allow nIndex for unauthorized users
+   if not auth.has_capability(auth.capabilities.historical_flows) then
+      return false
+   end
+
    -- TODO optimize
    if prefs == nil then
       prefs = ntop.getPrefs()