Make sure we create a grab pass buffer if no source is present (#4593)
Make sure we create a grab pass buffer if no source is present (#4593)

* Make sure we create a grab pass buffer if no source is present

* Refactor

Get the requested size from either the device or the requested render target, and compare that with, if present, the existing render target to figure out whether or not we need to resize (or initialise)

* Remove extra check
MicroWorldwide/PlayCanvas,playcanvas/engine,MicroWorldwide/PlayCanvas,playcanvas/engine