message: Fix for CheckPOS when no initial block download triggered when synch
  Can happen immediately after a lot of PoW blocks were created (like in regtest mode), but no wait for time to pass in order the initial block download be triggered.
diff: @@ -4402,7 +4402,10 @@ bool CChainState::UpdateHashProof(const CBlock& block, CValidationState& state,
  bool CheckPOS(const CBlockHeader& block, CBlockIndex* pindexPrev)
  {
  // Determining if PoS is possible to be checked in the header
  - return pindexPrev && block.IsProofOfStake() && !IsInitialBlockDownload();
  + return pindexPrev && block.IsProofOfStake() && !IsInitialBlockDownload()
  + // Additional check if not triggered initial block download, like when PoW blocks were initially created
  + // CheckPOS is called after ContextualCheckBlockHeader where future block headers are not accepted
  + && (pindexPrev->nHeight + 1 - chainActive.Height() < COINBASE_MATURITY);
  }
  bool CChainState::AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex)
  