Merge bitcoin/bitcoin#30388: validation: Check if mempool exists before size check in ActivateSnapshot

33c48c1 validation: Check if mempool exists before asserting in ActivateSnapshot (TheCharlatan)

Pull request description:

  The mempool is an optional component of the chainstate manager, so don't assume its presence and instead check if it is there first.

ACKs for top commit:
  maflcko:
    re-ACK 33c48c1
  fjahr:
    ACK 33c48c1

Tree-SHA512: 7a3568d5b7af45efa7bf54bae7bac1f00dc99bc9d47a744d73594f283c952be9500168f680d72f4aee09761da4e878ddca83ba675cdea8ee9e44eeff00ac09da

Author: glozow

src/validation.cpp

@@ -5681,7 +5681,8 @@ util::Result<void> ChainstateManager::ActivateSnapshot(
             return util::Error{strprintf(_("The base block header (%s) is part of an invalid chain."), base_blockhash.ToString())};
         }
 
-        if (Assert(m_active_chainstate->GetMempool())->size() > 0) {
+        auto mempool{m_active_chainstate->GetMempool()};
+        if (mempool && mempool->size() > 0) {
             return util::Error{_("Can't activate a snapshot when mempool not empty.")};
         }
     }