Merge dashpay#6789: fix: avoid possible nullptr for unknown hash of qc after LookupBlockIndex

3b9e061 fix: handle possible nullptr in InitNewQuorum (Konstantin Akimov)
c7890b7 fix: avoid possible nullptr for unknown hash of qc after LookupBlockIndex (Konstantin Akimov)

Pull request description:

  ## Issue being fixed or feature implemented
  Follow-up for dashpay#6692; discovered possible nullptr usage after looking for non-existing block

  ## What was done?
  Added extra check for nullptr in 3 missing places in dash specific code:
   - CDKGSessionHandler::HandleDKGRound
   - CQuorumBlockProcessor::ProcessBlock
   - CQuorumBlockProcessor::ProcessCommitment

  ## How Has This Been Tested?
  N/A

  ## Breaking Changes
  N/A

  ## Checklist:
  - [x] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  UdjinM6:
    utACK 3b9e061

Tree-SHA512: 3e5fa925250efa0e272c25f39d833c8fd1e51f1b9a338a63e8940dadfb91c61933eb48196f588621fdda3106fb887bd311dd01c287549720adb6124503e26b79

Author: PastaPastaPasta

src/llmq/blockprocessor.cpp

@@ -272,6 +272,11 @@ bool CQuorumBlockProcessor::ProcessCommitment(int nHeight, const uint256& blockH
     }
 
     const auto* pQuorumBaseBlockIndex = m_chainstate.m_blockman.LookupBlockIndex(qc.quorumHash);
+    if (pQuorumBaseBlockIndex == nullptr) {
+        LogPrint(BCLog::LLMQ, "%s -- unexpectedly failed due to no known pindex for hash[%s]\n", __func__,
+                 qc.quorumHash.ToString());
+        return false;
+    }
 
     if (!qc.Verify(m_dmnman, m_qsnapman, pQuorumBaseBlockIndex, /*checkSigs=*/fBLSChecks)) {
         LogPrint(BCLog::LLMQ, "CQuorumBlockProcessor::%s height=%d, type=%d, quorumIndex=%d, quorumHash=%s, signers=%s, validMembers=%d, quorumPublicKey=%s qc verify failed.\n", __func__,

src/llmq/dkgsessionhandler.cpp

@@ -537,7 +537,7 @@ void CDKGSessionHandler::HandleDKGRound(CConnman& connman, PeerManager& peerman)
 
     const CBlockIndex* pQuorumBaseBlockIndex = WITH_LOCK(cs_main, return m_chainstate.m_blockman.LookupBlockIndex(curQuorumHash));
 
-    if (!InitNewQuorum(pQuorumBaseBlockIndex)) {
+    if (!pQuorumBaseBlockIndex || !InitNewQuorum(pQuorumBaseBlockIndex)) {
         // should actually never happen
         WaitForNewQuorum(curQuorumHash);
         throw AbortPhaseException();