update stac_io from owner root (#762)

* update stac_io from owner root

* updating CHANGELOG

* Update pystac/link.py

Adding @lossyrob suggestion to avoid root link from resolving when it is the root.

Co-authored-by: Rob Emanuele <rdemanuele@gmail.com>

Co-authored-by: Rob Emanuele <rdemanuele@gmail.com>
Co-authored-by: Jon Duckworth <duckontheweb@gmail.com>

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Added
 
 - Enum MediaType entry for PDF documents ([#758](https://github.com/stac-utils/pystac/pull/758)) 
+- Updated Link to obtain stac_io from owner root ([#762](https://github.com/stac-utils/pystac/pull/762))
 
 ### Removed
 

pystac/link.py

@@ -298,6 +298,10 @@ def resolve_stac_object(self, root: Optional["Catalog_Type"] = None) -> "Link":
                     if self.owner is not None:
                         if isinstance(self.owner, pystac.Catalog):
                             stac_io = self.owner._stac_io
+                        elif self.rel != pystac.RelType.ROOT:
+                            owner_root = self.owner.get_root()
+                            if owner_root is not None:
+                                stac_io = owner_root._stac_io
                     if stac_io is None:
                         stac_io = pystac.StacIO.default()