Bail on exception during delayed autoload

We shouldn't try to load further classes if one autoload throws.

This fixes oss-fuzz #38881, though I believe there are still two
deeper issues here: 1) Why do we allow autoloading with an active
exception? 2) Exception save & restore should probably also save
and restore the exception opline.

Zend/tests/exception_during_variance_autoload.phpt

@@ -0,0 +1,31 @@
+--TEST--
+Exception during delayed variance autoload
+--FILE--
+<?php
+spl_autoload_register(function($class) {
+    echo "$class\n";
+    if ($class == 'X') {
+        new Y;
+    }
+    if ($class == 'Y') {
+        new Q;
+    }
+});
+class A {
+    function method(): X {}
+}
+class B extends A {
+    function method(): Y {}
+}
+?>
+--EXPECTF--
+Y
+Q
+
+Warning: Uncaught Error: Class "Q" not found in %s:%d
+Stack trace:
+#0 %s(%d): {closure}('Y')
+#1 {main}
+  thrown in %s on line %d
+
+Fatal error: Could not check compatibility between B::method(): Y and A::method(): X, because class Y is not available in %s on line %d

Zend/zend_inheritance.c

@@ -2348,6 +2348,9 @@ static void load_delayed_classes() {
 
 	ZEND_HASH_FOREACH_STR_KEY(delayed_autoloads, name) {
 		zend_lookup_class(name);
+		if (EG(exception)) {
+			break;
+		}
 	} ZEND_HASH_FOREACH_END();
 
 	zend_hash_destroy(delayed_autoloads);