Fix opcache startup after a shutdown

SAPIs such as phpdbg may run multiple startup-shutdown cycles in the same
process.

Author: arnaud-lb

ext/opcache/ZendAccelerator.c

@@ -3485,6 +3485,8 @@ void accel_shutdown(void)
 	zend_ini_entry *ini_entry;
 	bool _file_cache_only = false;
 
+	accel_starting = false;
+
 #ifdef HAVE_JIT
 	zend_jit_shutdown();
 #endif

ext/opcache/zend_accelerator_module.c

@@ -453,6 +453,8 @@ static ZEND_MSHUTDOWN_FUNCTION(zend_accelerator)
 
 	UNREGISTER_INI_ENTRIES();
 	accel_shutdown();
+	accel_module_loaded = false;
+
 	return SUCCESS;
 }