Bug #26564: Windows implementation of pthread_join crashes

MySQL uses _beginthread()/_endthread() instead of 
_beginthreadex()/_endthreadex() to create/end its threads
on Windows.
According to MSDN  _endthread() does close the thread handle.
So there's no need the handle to be closed explicitly.
Besides : WaitForSingleObject(, INFINITE) != WAIT_OBJECT_0) is
true for all practical cases as the other two possible return 
codes (according to MSDN) cannot happen in that case the 
CloseHandle() was actually a dead code.
Fixed by removing the CloseHandle() call. No test case added
because it's not possible to test for absence of dead code. 

include/my_pthread.h

@@ -181,8 +181,7 @@ void pthread_exit(void *a);	 /* was #define pthread_exit(A) ExitThread(A)*/
 #define my_pthread_setprio(A,B)  SetThreadPriority(GetCurrentThread(), (B))
 #define pthread_kill(A,B) pthread_dummy(0)
 
-#define pthread_join(A,B) \
-  ((WaitForSingleObject((A), INFINITE) != WAIT_OBJECT_0) || !CloseHandle(A))
+#define pthread_join(A,B) (WaitForSingleObject((A), INFINITE) != WAIT_OBJECT_0)
 
 /* Dummy defines for easier code */
 #define pthread_attr_setdetachstate(A,B) pthread_dummy(0)