wallet: don't iter twice when getting the cached debit/credit amount #25544

A small optimization i stumbled upon while looking at something else. Figured it could be worth a PR.

Instead of calling GetCachableAmount twice, which will result in iterating through all the transaction txins/txouts and calling GetDebit/GetCredit (which lock cs_wallet), just merge the filters and do it once.

ACK 757216e31cac7dcd45e11b2a2c6148420b3b99da. Neat trick. I verified that the behavior does not change.

<details> <summary>Small suggestion</summary>

diff --git a/src/wallet/receive.cpp b/src/wallet/receive.cpp
index d3303c0b1..3df4adf03 100644
--- a/src/wallet/receive.cpp
+++ b/src/wallet/receive.cpp
@@ -129,7 +129,7 @@ CAmount CachedTxGetCredit(const CWallet& wallet, const CWalletTx& wtx, const ism
     if (wallet.IsTxImmatureCoinBase(wtx))
         return 0;
 
-    CAmount credit = 0;
+    CAmount credit{0};
     const isminefilter get_amount_filter{filter & ISMINE_ALL};
     if (get_amount_filter) {
         // GetBalance can assume transactions in mapWallet won't change
@@ -143,7 +143,7 @@ CAmount CachedTxGetDebit(const CWallet& wallet, const CWalletTx& wtx, const ismi
     if (wtx.tx->vin.empty())
         return 0;
 
-    CAmount debit = 0;
+    CAmount debit{0};
     const isminefilter get_amount_filter{filter & ISMINE_ALL};
     if (get_amount_filter) {
         debit += GetCachableAmount(wallet, wtx, CWalletTx::DEBIT, get_amount_filter);

</details>

ACK 757216e31cac7dcd45e11b2a2c6148420b3b99da