Check exception after QM_ASSIGN of undef var

While most other exceptions aren't possible when QM_ASSIGN is used
instead of ASSIGN, we still have to watch out for an undef var
notice being promoted to an exception.

ext/opcache/jit/zend_jit_x86.dasc

@@ -8790,6 +8790,9 @@ static int zend_jit_qm_assign(dasm_State **Dst, const zend_op *opline, uint32_t
 	if (!zend_jit_store_var_if_necessary(Dst, opline->result.var, res_addr, res_info)) {
 		return 0;
 	}
+	if (op1_info & MAY_BE_UNDEF) {
+		zend_jit_check_exception(Dst);
+	}
 	return 1;
 }
 

ext/opcache/tests/jit/qm_assign_undef_exception.phpt

@@ -0,0 +1,22 @@
+--TEST--
+QM_ASSIGN of undef var may throw exception
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.file_update_protection=0
+opcache.jit_buffer_size=1M
+--FILE--
+<?php
+set_error_handler(function($_, $m) { throw new Exception($m); });
+function test() {
+    $a = $b;
+    X;
+}
+try {
+    test();
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+Undefined variable $b