bug #39795 Dont allow unserializing classes with a destructor - 5.1 (jderusse)

This PR was merged into the 5.1 branch.

Discussion
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Dont allow unserializing classes with a destructor - 5.1

| Q             | A
| ------------- | ---
| Branch?       | 5.1
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Prevent destructors with side-effects from being unserialized

Commits
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07402f4af3 Dont allow unserializing classes with a destructor - 5.1

Author: nicolas-grekas

UnicodeString.php

@@ -359,6 +359,10 @@ public function startsWith($prefix): bool
 
     public function __wakeup()
     {
+        if (!\is_string($this->string)) {
+            throw new \BadMethodCallException('Cannot unserialize '.__CLASS__);
+        }
+
         normalizer_is_normalized($this->string) ?: $this->string = normalizer_normalize($this->string);
     }