core: InstanceDiff.ApplyToValue correctly handle creates
core: InstanceDiff.ApplyToValue correctly handle creates

We previously tried to take a shortcut for an empty diff, just returning
the given value directly. This is incorrect in the weird case where we're
creating a new instance but it has no attributes (and thus an empty diff)
because in that case we'd return the given null value, turning the result
into a no-op or destroy change.

To fix this, we just always do the work to construct a new value, even
if we might end up doing all this just to reconstruct the same value we
started with in some cases.

drebes/terraform,ewbankkit/terraform,rnaveiras/terraform,drebes/terraform,brandontosch/terraform,pradeepbhadani/terraform,rnaveiras/terraform,luis-silva/terraform,mattray/terraform,heimweh/terraform,iljaskevic/terraform,VladRassokhin/terraform,brandontosch/terraform,youhong316/terraform,gechr/terraform,pdecat/terraform,tpounds/terraform,apparentlymart/terraform,apparentlymart/terraform,hashicorp/terraform,luis-silva/terraform,drebes/terraform,apparentlymart/terraform,iljaskevic/terraform,heimweh/terraform,pryorda/terraform,ewbankkit/terraform,tommynsong/terraform,pdecat/terraform,tpounds/terraform,mattray/terraform,apparentlymart/terraform,youhong316/terraform,brandontosch/terraform,mattray/terraform,tpounds/terraform,heimweh/terraform,pryorda/terraform,tommynsong/terraform,gechr/terraform,VladRassokhin/terraform,brandontosch/terraform,mattray/terraform,luis-silva/terraform,hashicorp/terraform,iljaskevic/terraform,pdecat/terraform,youhong316/terraform,nlamirault/terraform,VladRassokhin/terraform,ewbankkit/terraform,pradeepbhadani/terraform,heimweh/terraform,brandontosch/terraform,tommynsong/terraform,pradeepbhadani/terraform,nlamirault/terraform,pdecat/terraform,luis-silva/terraform,hashicorp/terraform,heimweh/terraform,gechr/terraform,iljaskevic/terraform,apparentlymart/terraform,VladRassokhin/terraform,drebes/terraform,rnaveiras/terraform,nlamirault/terraform,ewbankkit/terraform,youhong316/terraform,pryorda/terraform,tpounds/terraform