validation: don't use GetAll() in CheckBlockIndex()

GetAll() is non-const, preventing CheckBlockIndex() from being
const. Rather than add a const GetAll() method, just iterate over
the chainstates directly.

Slight behaviour change by also subjecting non-`IsUsable()`
chainstates to consistency checks.

Author: stickies-v

src/validation.cpp

@@ -5354,8 +5354,8 @@ void ChainstateManager::CheckBlockIndex()
         if (pindex->pprev == nullptr) {
             // Genesis block checks.
             assert(pindex->GetBlockHash() == GetConsensus().hashGenesisBlock); // Genesis block's hash must match.
-            for (auto c : GetAll()) {
-                if (c->m_chain.Genesis() != nullptr) {
+            for (const Chainstate* c : {m_ibd_chainstate.get(), m_snapshot_chainstate.get()}) {
+                if (c && c->m_chain.Genesis() != nullptr) {
                     assert(pindex == c->m_chain.Genesis()); // The chain's genesis block must be this block.
                 }
             }
@@ -5408,8 +5408,8 @@ void ChainstateManager::CheckBlockIndex()
         }
 
         // Chainstate-specific checks on setBlockIndexCandidates
-        for (auto c : GetAll()) {
-            if (c->m_chain.Tip() == nullptr) continue;
+        for (const Chainstate* c : {m_ibd_chainstate.get(), m_snapshot_chainstate.get()}) {
+            if (!c || c->m_chain.Tip() == nullptr) continue;
             // Two main factors determine whether pindex is a candidate in
             // setBlockIndexCandidates:
             //
@@ -5492,7 +5492,8 @@ void ChainstateManager::CheckBlockIndex()
             //    tip.
             // So if this block is itself better than any m_chain.Tip() and it wasn't in
             // setBlockIndexCandidates, then it must be in m_blocks_unlinked.
-            for (auto c : GetAll()) {
+            for (const Chainstate* c : {m_ibd_chainstate.get(), m_snapshot_chainstate.get()}) {
+                if (!c) continue;
                 const bool is_active = c == &ActiveChainstate();
                 if (!CBlockIndexWorkComparator()(pindex, c->m_chain.Tip()) && c->setBlockIndexCandidates.count(pindex) == 0) {
                     if (pindexFirstInvalid == nullptr) {