[php-src] Issue #21376: gzfile and readgzfile no longer identify corrupted gzip data

Issue: https://github.com/php/php-src/issues/21376
Author: splitbrain

### Description

Using this (invalid) gzip file: [corrupt.txt.gz](https://github.com/user-attachments/files/25815648/corrupt.txt.gz) for testing below.

> Just for completion: this is what happens using zcat/gzip - it can't decode it and thinks it's encrypted. It's not, it's just garbage.
> ```
> $ zcat corrupt.txt.gz
> gzip: corrupt.txt.gz is encrypted -- not supported
> ```

The following code:

```php
<?php
var_dump(gzfile("corrupt.txt.gz"));
```

Resulted in this output:
```
array(2) {
  [0]=>
  string(8) "x��	U"
  [1]=>
  string(6) "I-.��"
}
```

But I expected this output instead:
```
array(0) {
}
```

Running the same code with PHP < 8.5.3 (including 8.5.2) will result in the expected empty array.

The same issue exists when using `readgzfile()`: all older versions will return `-1` while 8.5.3 returns binary data.



### PHP Version

```plain
PHP 8.5.3 (cli) (built: Feb 12 2026 16:29:14) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.5.3, Copyright (c) Zend Technologies
    with Xdebug v3.5.1, Copyright (c) 2002-2026, by Derick Rethans
    with Zend OPcache v8.5.3, Copyright (c), by Zend Technologies
```

### Operating System

ArchLinux