Only call NotifyBlockTip when the active chain changes
Only call NotifyBlockTip when the active chain changes

Previously, if `invalidateblock` was called on a block in a branch,
NotifyBlockTip would be called on that block's predecessor, creating an
incorrect `rpc/blockchain.cpp:latestblock` value.

Only call NotifyBlockTip if the chain being modified is activeChain.

peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin