Bugfix: Don't check the genesis block header before accepting it

This fixes an error triggered when running with -reindex after #5975

src/main.cpp

@@ -2809,36 +2809,37 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
     uint256 hash = block.GetHash();
     BlockMap::iterator miSelf = mapBlockIndex.find(hash);
     CBlockIndex *pindex = NULL;
-    if (miSelf != mapBlockIndex.end()) {
-        // Block header is already known.
-        pindex = miSelf->second;
-        if (ppindex)
-            *ppindex = pindex;
-        if (pindex->nStatus & BLOCK_FAILED_MASK)
-            return state.Invalid(error("%s: block is marked invalid", __func__), 0, "duplicate");
-        return true;
-    }
+    if (hash != chainparams.GetConsensus().hashGenesisBlock) {
 
-    if (!CheckBlockHeader(block, state))
-        return false;
+        if (miSelf != mapBlockIndex.end()) {
+            // Block header is already known.
+            pindex = miSelf->second;
+            if (ppindex)
+                *ppindex = pindex;
+            if (pindex->nStatus & BLOCK_FAILED_MASK)
+                return state.Invalid(error("%s: block is marked invalid", __func__), 0, "duplicate");
+            return true;
+        }
 
-    // Get prev block index
-    CBlockIndex* pindexPrev = NULL;
-    if (hash != chainparams.GetConsensus().hashGenesisBlock) {
+        if (!CheckBlockHeader(block, state))
+            return false;
+
+        // Get prev block index
+        CBlockIndex* pindexPrev = NULL;
         BlockMap::iterator mi = mapBlockIndex.find(block.hashPrevBlock);
         if (mi == mapBlockIndex.end())
             return state.DoS(10, error("%s: prev block not found", __func__), 0, "bad-prevblk");
         pindexPrev = (*mi).second;
         if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
             return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
-    }
-    assert(pindexPrev);
-    if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, hash))
-        return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
 
-    if (!ContextualCheckBlockHeader(block, state, pindexPrev))
-        return false;
+        assert(pindexPrev);
+        if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, hash))
+            return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
 
+        if (!ContextualCheckBlockHeader(block, state, pindexPrev))
+            return false;
+    }
     if (pindex == NULL)
         pindex = AddToBlockIndex(block);