Win32 threads: fix memory leak of detached thread

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit b1f9242606caf549a03c6b11b00c66c2c1af27cb)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

src/win32/thread.c

@@ -503,7 +503,10 @@ static int vlc_clone_attr (vlc_thread_t *p_handle, bool detached,
     }
 
     if (detached)
+    {
         CloseHandle((HANDLE)h);
+        th->id = NULL;
+    }
     else
         th->id = (HANDLE)h;