is_numeric和trim导致的判断绕过

<?php
if(isset($_GET['source'])){
    highlight_file(__FILE__);
    exit;
}
include_once("flag.php");
 /*
    shougong check if the $number is a palindrome number(hui wen shu)
 */
function is_palindrome_number($number) {
    $number = strval($number);
    $i = 0;
    $j = strlen($number) - 1;
    while($i < $j) {
        if($number[$i] !== $number[$j]) {
            return false;
        }
        $i++;
        $j--;
    }
    return true;
}
ini_set("display_error", false);
error_reporting(0);
$info = "";
$req = [];
foreach([$_GET, $_POST] as $global_var) {
    foreach($global_var as $key => $value) {
        $value = trim($value);
        is_string($value) && is_numeric($value) && $req[$key] = addslashes($value);
    }
}    
 
$n1 = intval($req["number"]);
$n2 = intval(strrev($req["number"]));
if($n1 && $n2) {
    if ($req["number"] != intval($req["number"])) {
        $info = "number must be integer!";
    } elseif ($req["number"][0] == "+" || $req["number"][0] == "-") {
        $info = "no symbol";
    } elseif ($n1 != $n2) { //first check
        $info = "no, this is not a palindrome number!";
    } else { //second check
        if(is_palindrome_number($req["number"])) {
            $info = "nice! {$n1} is a palindrome number!";
        } else {
            if(strpos($req["number"], ".") === false && $n1 < 2147483646) {
                $info = "find another strange dongxi: " . FLAG2;
            } else {
                $info = "find a strange dongxi: " . FLAG;
            }
        }
    }
} else {
    $info = "no number input~";
}
?>