Move mempool nullptr Assert out of LoadChainstate

Summary:
Partial backport of [[bitcoin/bitcoin#23280 | core#23280]]:
bitcoin/bitcoin@8715658

Depends on D12566.

Test Plan:
  ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12567

Author: Fabcien

src/init.cpp

@@ -2466,9 +2466,9 @@ bool AppInitMain(Config &config, RPCServer &rpcServer,
         const int64_t load_block_index_start_time = GetTimeMillis();
 
         auto rv =
-            LoadChainstate(fReset, chainman, node.mempool.get(), fPruneMode,
-                           config, fReindexChainState, nBlockTreeDBCache,
-                           nCoinDBCache, nCoinCacheUsage,
+            LoadChainstate(fReset, chainman, Assert(node.mempool.get()),
+                           fPruneMode, config, fReindexChainState,
+                           nBlockTreeDBCache, nCoinDBCache, nCoinCacheUsage,
                            args.GetIntArg("-checkblocks", DEFAULT_CHECKBLOCKS),
                            args.GetIntArg("-checklevel", DEFAULT_CHECKLEVEL));
 

src/node/chainstate.cpp

@@ -30,7 +30,7 @@ LoadChainstate(bool fReset, ChainstateManager &chainman, CTxMemPool *mempool,
     do {
         try {
             LOCK(cs_main);
-            chainman.InitializeChainstate(Assert(mempool));
+            chainman.InitializeChainstate(mempool);
             chainman.m_total_coinstip_cache = nCoinCacheUsage;
             chainman.m_total_coinsdb_cache = nCoinDBCache;