We have cache update mechanism (Neo's cache votesChanged flag), it must
be used for current epoch and new epoch cached values update. And the
cached current/new epoch values themselves must always contain valid
information for the current/new epoch. These cached values must only be
changed once per epoch, never set them to nil.
This commit prevents CN node panic described in #3253 when dBFT tries
to retrieve new epoch validators with some votes modifications made
before at the same dBFT epoch.
Close#3253.
Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>
d7d850ac7d