fix the bug

src/coroutine/coroutine.cc

@@ -2,9 +2,11 @@
 
 using study::Coroutine;
 
+Coroutine* Coroutine::current = nullptr;
+
 void* Coroutine::get_current_task()
 {
-    return Coroutine::current ? Coroutine::current->get_task() : nullptr;
+    return current ? current->get_task() : nullptr;
 }
 
 void* Coroutine::get_task()

study_coroutine.cc

@@ -3,6 +3,8 @@
 using study::PHPCoroutine;
 using study::Coroutine;
 
+php_coro_task PHPCoroutine::main_task = {0};
+
 long PHPCoroutine::create(zend_fcall_info_cache *fci_cache, uint32_t argc, zval *argv)
 {
     php_coro_args php_coro_args;