Add regression test for bug #81705

Co-authored-by: cmbecker69@gmx.de
Co-authored-by: yukik@risec.co.jp

Author: nielsdos

Zend/tests/bug81705.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Bug #81705 (type confusion/UAF on set_error_handler with concat operation)
+--FILE--
+<?php
+
+$arr = [0];
+$my_var = str_repeat("a", 1);
+set_error_handler(
+    function() use(&$my_var) {
+        echo("error\n");
+        $my_var = 0x123;
+    }
+);
+$my_var .= $GLOBALS["arr"];
+var_dump($my_var);
+?>
+--EXPECT--
+error
+string(6) "aArray"