SF: Don't enable expensive rendering for unknown dataspace

Layer dataspace is initialized as unknown by default, unless
overriden by the buffer source. We don't require expensive
rendering for color conversion when the dataspace is unknown.

Change-Id: I079c520f63a65c77ba3162664656e607eafff991
Signed-off-by: Simão Gomes Viana <devel@superboring.dev>