Merge #20868: validation: remove redundant check on pindex

c943282 validation: remove redundant check on pindex (jarolrod)

Pull request description:

  This removes a redundant check on `pindex` being a `nullptr`. By the time we get to this step `pindex` is always a `nullptr` as the branch where it has been set would have already returned.

  Closes #19223

ACKs for top commit:
  Zero-1729:
    re-ACK c943282
  ajtowns:
    ACK c943282 - code review only
  MarcoFalke:
    review ACK c943282 📨
  theStack:
    re-ACK c943282

Tree-SHA512: d2dc58206be61d2897b0703ee93af67abed492a80e84ea03dcfbf7116833173da3bdafa18ff80422d5296729d5254d57cc1db03fdaf817c8f57c62c3abef673c

Author: MarcoFalke

src/validation.cpp

@@ -3558,11 +3558,10 @@ bool BlockManager::AcceptBlockHeader(const CBlockHeader& block, BlockValidationS
     // Check for duplicate
     uint256 hash = block.GetHash();
     BlockMap::iterator miSelf = m_block_index.find(hash);
-    CBlockIndex *pindex = nullptr;
     if (hash != chainparams.GetConsensus().hashGenesisBlock) {
         if (miSelf != m_block_index.end()) {
             // Block header is already known.
-            pindex = miSelf->second;
+            CBlockIndex* pindex = miSelf->second;
             if (ppindex)
                 *ppindex = pindex;
             if (pindex->nStatus & BLOCK_FAILED_MASK) {
@@ -3631,8 +3630,7 @@ bool BlockManager::AcceptBlockHeader(const CBlockHeader& block, BlockValidationS
             }
         }
     }
-    if (pindex == nullptr)
-        pindex = AddToBlockIndex(block);
+    CBlockIndex* pindex = AddToBlockIndex(block);
 
     if (ppindex)
         *ppindex = pindex;