libpod: read mappings when joining a container userns

when joining an existing container user namespace, read the existing
mappings so the storage can be created with the correct ownership.

Closes: https://github.com/containers/podman/issues/7547

Signed-off-by: Giuseppe Scrivano <giuseppe@scrivano.org>

libpod/container_internal.go

@@ -380,6 +380,8 @@ func (c *Container) setupStorageMapping(dest, from *storage.IDMappingOptions) {
 			}
 			dest.GIDMap = append(dest.GIDMap, g)
 		}
+		dest.HostUIDMapping = false
+		dest.HostGIDMapping = false
 	}
 }