[BW]: [Fix] fc::task_base class member initialization.

include/fc/thread/task.hpp

@@ -13,7 +13,7 @@ namespace fc {
       void        run(); 
     protected:
       ~task_base();
-
+      /// Task priority looks like unsupported feature.
       uint64_t    _posted_num;
       priority    _prio;
       time_point  _when;

src/thread/task.cpp

@@ -9,7 +9,12 @@
 
 namespace fc {
   task_base::task_base(void* func)
-  :_functor(func){
+  :
+  _posted_num(0),
+  _active_context(nullptr),
+  _next(nullptr),
+  _promise_impl(nullptr),
+  _functor(func){
   }
 
   void task_base::run() {