Fix Lua syntax error in co_wan function

- Split complex one-liner into multiple statements
- Fix: or "":find() caused parse error

package/src/client2server-unified.lua

@@ -504,12 +504,12 @@ local function co_wan()
     local link_last, ip_last = nil, nil
     
     local f = io.open("/sys/class/net/" .. cfg.wan_device .. "/carrier", "r")
-    if f then link_last = (f:read("*a") or "":find("^1") == 1; f:close() end
+    if f then local content = f:read("*a") or ""; link_last = content:find("^1") == 1; f:close() end
     
     while true do
         -- Link
         f = io.open("/sys/class/net/" .. cfg.wan_device .. "/carrier", "r")
-        local link_now = f and ((f:read("*a") or ""):find("^1") == 1) or false
+        local content = f and f:read("*a") or ""; local link_now = content:find("^1") == 1 or false
         if f then f:close() end
         
         if link_now ~= link_last then