Stop trimming when mapTx is empty

src/txmempool.cpp

@@ -1075,7 +1075,7 @@ void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRe
 
     unsigned nTxnRemoved = 0;
     CFeeRate maxFeeRateRemoved(0);
-    while (DynamicMemoryUsage() > sizelimit) {
+    while (!mapTx.empty() && DynamicMemoryUsage() > sizelimit) {
         indexed_transaction_set::index<descendant_score>::type::iterator it = mapTx.get<descendant_score>().begin();
 
         // We set the new mempool min fee to the feerate of the removed set, plus the