[C++] Fix the compiling warning issue

components/cplusplus/Thread.cpp

@@ -6,7 +6,7 @@ Thread::Thread(rt_uint32_t stack_size,
                rt_uint8_t  priority,
                rt_uint32_t tick,
                const char *name)
-: _entry(RT_NULL), started(false)
+: _entry(RT_NULL), _param(RT_NULL), started(false)
 {
     rt_event_init(&_event, name, 0);
 
@@ -24,7 +24,7 @@ Thread::Thread(void (*entry)(void *p),
                rt_uint8_t  priority,
                rt_uint32_t tick,
                const char *name)
-: _entry(RT_NULL), started(false), _param(p)
+: _entry(RT_NULL), _param(p), started(false)
 {
     rt_event_init(&_event, name, 0);