We must only return early in cases where we received a roster push with
1. a `from` attribute
2. that `from` is not our bare JID
The server sends roster pushes without `from` attribute and we must accept
them.
Fixes#2035
Fixes: bac24601da ("Introduce `equals_our_barejid()`")
Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>