Fix backbuffer RTV not recreating properly if Desc->Format is UNKNOWN
Fix backbuffer RTV not recreating properly if Desc->Format is UNKNOWN

* Judging by the error reports that pointed to this crash, this happens
  with the Dolphin emulator.

adrianbu/renderdoc,googlestadia/renderdoc,adrianbu/renderdoc,adrianbu/renderdoc,cgmb/renderdoc,moradin/renderdoc,googlestadia/renderdoc,etnlGD/renderdoc,michaelrgb/renderdoc,Velro/renderdoc,adrianbu/renderdoc,etnlGD/renderdoc,Anteru/renderdoc,Zorro666/renderdoc,Anteru/renderdoc,TurtleRockStudios/renderdoc_public,victor-moya/renderdoc,victor-moya/renderdoc,moradin/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public,Zorro666/renderdoc,Zorro666/renderdoc,michaelrgb/renderdoc,Velro/renderdoc,Anteru/renderdoc,TurtleRockStudios/renderdoc_public,Yours3lf/renderdoc,cgmb/renderdoc,Yours3lf/renderdoc,googlestadia/renderdoc,TurtleRockStudios/renderdoc_public,etnlGD/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,Anteru/renderdoc,victor-moya/renderdoc,moradin/renderdoc,Lssikkes/renderdoc,victor-moya/renderdoc,Yours3lf/renderdoc,googlestadia/renderdoc,Lssikkes/renderdoc,Anteru/renderdoc,victor-moya/renderdoc,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,cgmb/renderdoc,michaelrgb/renderdoc,googlestadia/renderdoc,etnlGD/renderdoc,michaelrgb/renderdoc,Lssikkes/renderdoc,cgmb/renderdoc,moradin/renderdoc,victor-moya/renderdoc,baldurk/renderdoc,Velro/renderdoc,baldurk/renderdoc,TurtleRockStudios/renderdoc_public,etnlGD/renderdoc,Yours3lf/renderdoc,etnlGD/renderdoc,Lssikkes/renderdoc,Lssikkes/renderdoc,Lssikkes/renderdoc,Yours3lf/renderdoc,Anteru/renderdoc,adrianbu/renderdoc,Anteru/renderdoc,moradin/renderdoc,Velro/renderdoc,Velro/renderdoc,cgmb/renderdoc,googlestadia/renderdoc,Velro/renderdoc,baldurk/renderdoc,moradin/renderdoc,adrianbu/renderdoc,Yours3lf/renderdoc,michaelrgb/renderdoc