text: Title: Getting/Setting slider  values on OBS Studio 64
  Body: I'm trying to get/set the range of a volume slider on OBS Studio 64 bit. https://obsproject.com/download
  I'm on the latest version `21.1.2`. Here is my code:
  
  ```python
  from pywinauto.application import Application
  
  app = Application(backend='uia').connect(path='obs64.exe')
  
  # Mixers area
  mixers = app.top_window().child_window(title="Mixer", control_type="Window")
  
  # the volume slider
  slider = mixers.child_window(
      title_re="Volume slider for 'Desktop Audio'",
      control_type="Slider"
  )
  slider_wrapper = slider.wrapper_object()
  print(slider_wrapper.min_value())
  ```
  
  Here's the exception:
  
  ```
  Traceback (most recent call last):
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\pywinauto\uia_defines.py", line 232, in get_elem_interface
      iface = cur_ptrn.QueryInterface(cls_name)
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\comtypes\__init__.py", line 1158, in QueryInterface
      self.__com_QueryInterface(byref(iid), byref(p))
  ValueError: NULL COM pointer access
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "c:/Users/glenbot/Documents/code/simple-stream-deck/test.py", line 55, in <module>
      print(slider_wrapper.min_value())
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\pywinauto\controls\uia_controls.py", line 434, in min_value
      return self.iface_range_value.CurrentMinimum
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\pywinauto\controls\uiawrapper.py", line 131, in __get__
      value = self.fget(obj)
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\pywinauto\controls\uiawrapper.py", line 258, in iface_range_value
      return uia_defs.get_elem_interface(elem, "RangeValue")
    File "C:\Users\glenbot\AppData\Local\Programs\Python\Python36\lib\site-packages\pywinauto\uia_defines.py", line 234, in get_elem_interface
      raise NoPatternInterfaceError()
  pywinauto.uia_defines.NoPatternInterfaceError
  ```
  I have attempted to set the slider using coordinates but the resolution of the click matched to decibel value gets difficult to predict. I would rather call `set_value()` but I get the same error. Any help would be appreciated :)
  
  
  