check max_allowed_stack_size during startup

see #237

README.md

@@ -53,6 +53,18 @@ server can use it to call any native library they have access to.
 Of course if attackers are running their own PHP code on your webserver you
 are probably already toast, unfortunately.
 
+Finally, on php 8.3 and later you need to disable stack overflow
+tests. php-vips executes FFI callbacks off the main thread and this confuses
+those checks, at least in php 8.3.0.
+
+Add:
+
+```
+zend.max_allowed_stack_size=-1
+```
+
+To your `php.ini`.
+
 ### Example
 
 ```php

src/FFI.php

@@ -236,13 +236,17 @@ private static function init(): void
             return;
         }
 
-        // the two usual installation problems
+        // detect the most common installation problems
         if (!extension_loaded('ffi')) {
             throw new Exception('FFI extension not loaded');
         }
         if (!ini_get('ffi.enable')) {
             throw new Exception("ffi.enable not set to 'true'");
         }
+        if (version_compare(PHP_VERSION, '8.3') &&
+            ini_get('zend.max_allowed_stack_size') != '-1') {
+            throw new Exception("zend.max_allowed_stack_size not set to '-1'");
+        }
 
         $vips_libname = self::libraryName("libvips", 42);
         if (PHP_OS_FAMILY === "Windows") {