Merge #11132: Document assumptions that are being made to avoid NULL pointer dereferences

fdc3293 Document assumptions that are being made to avoid NULL pointer dereferences (practicalswift)

Pull request description:

  Document assumptions (via `assert(…)`:s) that are being made avoid `NULL` pointer dereferences.

  Rationale:
  * Make it clear to human reviewers and non-human static analyzers that what might look like potential `NULL` pointer dereferences are written the way they are intentionally (these cases are currently flagged by various static analyzers).

Tree-SHA512: b424328195e2680e1e4ec546298f718c49e5ad182147dc004de580693db1b50eec4065e1c4f232bdb302baa12954265a50ba21cb5ba4ff30248535b2de778672

src/validation.cpp

@@ -1711,6 +1711,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
     // before the first had been spent.  Since those coinbases are sufficiently buried its no longer possible to create further
     // duplicate transactions descending from the known pairs either.
     // If we're on the known chain at height greater than where BIP34 activated, we can save the db accesses needed for the BIP30 check.
+    assert(pindex->pprev);
     CBlockIndex *pindexBIP34height = pindex->pprev->GetAncestor(chainparams.GetConsensus().BIP34Height);
     //Only continue to enforce if we're below BIP34 activation height or the block hash at that height doesn't correspond.
     fEnforceBIP30 = fEnforceBIP30 && (!pindexBIP34height || !(pindexBIP34height->GetBlockHash() == chainparams.GetConsensus().BIP34Hash));
@@ -1850,6 +1851,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
         if (!pblocktree->WriteTxIndex(vPos))
             return AbortNode(state, "Failed to write transaction index");
 
+    assert(pindex->phashBlock);
     // add this block to the view's block chain
     view.SetBestBlock(pindex->GetBlockHash());