The obs_source::async_reset_texture variable can cause a data race
between threads to occur because it could be set to true in one thread
then changed back to false in another thread.  This could cause the
async texture to not update its size when it's supposed to, which can
cause a crash or corruption when copying data from a frame of a
differing size.

The solution to this is to:

- Delete the async_reset_texture variable, and make the
  set_async_texture_size function change the texture size if the
  async_width, async_height, or async_format variables differ from the
  frame's width/height/format.  Those variables are then only ever set
  in the libobs graphics thread.

- Make the cache_video function use separate variables from other
  functions to detect a change in size (due to the fact that the texture
  size should only be resized in the libobs graphics thread).  These
  variables are async_cache_width, async_cache_height, and
  async_cache_format, which are only be set in the thread that calls
  obs_source_output_video.

How to replicate the data race:

- On OSX, use window capture on a textedit window, then continually
  resize the textedit window.