undeleted relations don't show in relations panel

[malenki]

How to reproduce:

• undelete a relation or revert a changeset in which a relation is deleted
• have a look at the relations panel – it's empty

(Though you can "see" the relation with selecting all data)

Tested with

• undeleting ​https://www.openstreetmap.org/relation/1310659
• reverting ​https://www.openstreetmap.org/changeset/15933811

factory-default ~/.josm
r7968
java version "1.7.0_65"
OpenJDK Runtime Environment (IcedTea 2.5.3) (7u71-2.5.3-2)
OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)

See also:
https://josm.openstreetmap.de/ticket/5778#comment:12
#10986