vrend: force temp buffers for BGR* swizzles on small iovec transfers
@gerddie I found 4 SkQP tests still failing after !539 (merged) and tracked it to accidental swizzling of iovec backing buffers instead of temp buffers for small BGR* resources.
Forcing the use of temp buffers when (vrend_state.use_gles && vrend_format_is_bgra(res))
was enough to resolve it.
Closes #221 (closed)
Edited by Ryan Neph