Simplify the index handling for moving to the next or previous message.
Same for moving to the next or previous search results. Moving of the
index variable relies on the iterator package's StartIndex and EndIndex
functions.
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>
Extract the index acrobatics from the message store and move it to
iterator package for re-use and to add unit tests.
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>