Add test for bug #80039

This has already been fixed by 247105ae1a,
but let's add the additional test case.

Zend/tests/bug80039.phpt

@@ -0,0 +1,43 @@
+--TEST--
+Bug #80039: Illegal string offset and Cannot create references to/from string offsets
+--FILE--
+<?php
+
+final class A
+{
+	public string $a;
+
+	public static function fromArray(array $props): self
+	{
+		$me = new static;
+		foreach ($props as $k => &$v) {
+			$me->{$k} = &$v;
+		}
+		return $me;
+	}
+
+	public function __get($name)
+	{
+		throw new \LogicException("Property '$name' is not defined.");
+	}
+}
+
+class ObjectHelpers
+{
+	public static function hasProperty(string $class, string $name)
+	{
+		static $cache = [];
+		$prop = &$cache[$class][$name];  # <-- emits error
+        var_dump($prop);
+	}
+}
+
+set_exception_handler(function ($e) {
+	ObjectHelpers::hasProperty(A::class, 'a');
+});
+
+A::fromArray(['a' => 'foo']);
+
+?>
+--EXPECT--
+NULL