Fix ISSET_ISEMPTY_VAR missoptimization

This fixes oss-fuzz #46909

Author: dstogov

Zend/Optimizer/zend_optimizer.c

@@ -323,6 +323,8 @@ int zend_optimizer_update_op1_const(zend_op_array *op_array,
 		case ZEND_FETCH_IS:
 		case ZEND_FETCH_UNSET:
 		case ZEND_FETCH_FUNC_ARG:
+		case ZEND_ISSET_ISEMPTY_VAR:
+		case ZEND_UNSET_VAR:
 			TO_STRING_NOWARN(val);
 			if (opline->opcode == ZEND_CONCAT && opline->op2_type == IS_CONST) {
 				opline->opcode = ZEND_FAST_CONCAT;

ext/opcache/tests/opt/isset_var_001.phpt

@@ -0,0 +1,19 @@
+--TEST--
+ISSET_ISEMPTY_VAR 001: CONST operand of ISSET_ISEMPTY_VAR must be converted to STRING
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=-1
+--FILE--
+<?php
+class A {
+    function __destruct() {
+        $i=0;
+        if (isset($GLOBALS[$i])) y;
+    }
+}
+new A;
+?>
+DONE
+--EXPECT--
+DONE