message: getblockchaininfo: Fix case of pruning enabled but not pruned yet
  This skips adding the 'pruneheight' entry when the blockchain is
  marked as pruned but no blocks have been pruned yet. This might be a
  state that is never reached.
  (from clang static analysis)
diff: @@ -817,6 +817,7 @@ UniValue getblockchaininfo(const UniValue &params, bool fHelp)
  while (block && block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA))
  block = block->pprev;
  + if (block != nullptr)
  obj.push_back(Pair("pruneheight", block->nHeight));
  }
  return obj;
  