[REFACTOR] Initialize PrecomputedTransactionData in CheckInputScripts

Add a default constructor to `PrecomputedTransactionData`, which doesn't
initialize the struct's members. Instead they're initialized inside the
`CheckInputScripts()` function. This allows a later commit to add the
spent UTXOs to that structure.

src/script/interpreter.h

@@ -121,7 +121,12 @@ bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned i
 struct PrecomputedTransactionData
 {
     uint256 hashPrevouts, hashSequence, hashOutputs;
-    bool ready = false;
+    bool m_ready = false;
+
+    PrecomputedTransactionData() = default;
+
+    template <class T>
+    void Init(const T& tx);
 
     template <class T>
     explicit PrecomputedTransactionData(const T& tx);