remove excessive error messages:

  - do not print "MonitorFromWindow failed" in case when no error occurred (possibly a window is invisible to the user and does not reside on any concrete screen)
  - consider 0 returned by GetWindowLong[Ex] a valid value (it may be, particularly when we retrieve extended window styles)
fix Windows error logging:

  - do not leak memory
  - include `setlocale` call to prevent problems with printing of localized error messages to `wcerr` (on my system `wcerr` just stops printing anything after cyrillic symbols are sent to it)
Try to focus desktop after minimizing all windows.

Currently tested on Win7 only.