Windows: fd_to_winfd() shouldn't treat fd 0 as invalid

* fd_to_winfd() currently returns INVALID_WINFD if fd is 0, but usbi_create_fd()
  can legally assign an fd number of 0 if poll_fd[0] is not already occupied.
* Transfers which are assigned an fd number of 0 for their event handle are then
  unable to have their event handle retrieved later on.

See http://libusbx.1081486.n5.nabble.com/Libusbx-devel-PATCH-1-1-Windows-fd-to-winfd-shouldn-t-treat-fd-0-as-invalid-tt1535.html
WinCE: Fix race between wince_clock_gettime_threaded() and wince_clock_gettime()

* When the timer thread is created in wince_init(), it performs an initialisation
  phase in which it uses QueryPerformanceFrequency() to determine if there is a
  high resolution timer available, and sets hires_frequency and hires_ticks_to_ps
  appropriately. However, since wince_init() does not wait for this initialisation
  phase to complete, wince_clock_gettime() can be called before hires_frequency
  and hires_ticks_to_ps have been updated. This can result in
  wince_clock_gettime() temporarily returning real-time clock values even though
  the platform supports a monotonic clock.
* See http://sourceforge.net/mailarchive/forum.php?thread_name=1373619997-3535-1-git-send-email-simon.haggett%40realvnc.com&forum_name=libusbx-devel
Windows: Fix race between windows_clock_gettime_threaded() and windows_clock_gettime()

* When the timer thread is created in windows_init(), it performs an
  initialisation phase in which it uses QueryPerformanceFrequency() to determine
  if there is a high resolution timer available, and sets hires_frequency and
  hires_ticks_to_ps appropriately. However, since windows_init() does not wait for
  this initialisation phase to complete, windows_clock_gettime() can be called
  before hires_frequency and hires_ticks_to_ps have been updated. This can result
  in windows_clock_gettime() temporarily returning real-time clock values even
  though the platform supports a monotonic clock.
* See http://sourceforge.net/mailarchive/forum.php?thread_name=1373620013-3574-1-git-send-email-simon.haggett%40realvnc.com&forum_name=libusbx-devel