Fix crashes when anonymizing Spark

[reubenyap]

Wallet crashes at times when clicking on Anonymize All or when sending transparent balance to a Spark Address that you own.

PR intention

DeleteMe: Mandatory: What this PR is intended to do, what change it introduces, what issue it solves.

Complete Summary of All Bugs Fixed

Critical Bug (from PR #1734): Uninitialized Transaction in sparkwallet.cpp
Location: src/spark/sparkwallet.cpp, line 1206
Problem: The code was calling mempool.IsTransactionAllowed(*wtx.tx, state) where wtx.tx was still pointing to an empty/uninitialized transaction. The actual signed transaction (txNewConst) was created at line 1186, but wtx.tx is only set at line 1212 (AFTER the mempool check).
Root Cause: When mempool.IsTransactionAllowed() tried to access fields of the empty transaction, it caused EXCEPTION_ACCESS_VIOLATION.
Fix: Changed to use txNewConst (the actual signed transaction) instead of *wtx.tx.

Critical Null Pointer Bugs in wallet.cpp:

Location	Issue	Fix
Line 7168	CWallet::CreateSparkMintTransactions accessed sparkWallet-> without null check	Added null check with error return
Lines 4886, 4902	CreateSparkSpendTransaction and CreateSparkNameTransaction called EnsureMintWalletAvailable() instead of EnsureSparkWalletAvailable()	Changed to call the correct function
Line 1839	GetChange() accessed sparkWallet->getMyCoinV() without null check	Added null check
Line 1496	AbandonSpends() called on potentially null sparkWallet	Added null check
Line 1520	AbandonSparkMints() called on potentially null sparkWallet	Added null check
Line 2718	getMyCoinIsChange() called on potentially null sparkWallet	Added null check

Previously Fixed Bugs:

File	Issue	Fix
sparkwallet.cpp (line 1206)	PR #1734 bug - using uninitialized wtx.tx instead of txNewConst	Changed to use txNewConst
sendcoinsdialog.cpp (line 419)	Dangling entry pointer	Use static method call
sendcoinsdialog.cpp (lines 691-692)	Only updated one entry instead of all	Iterate over all entries
sparkmodel.cpp (line 109)	Null pointer on sparkWallet	Added null check
walletmodeltransaction.cpp (line 71)	Null pointer on sparkWallet	Added null check
transactionrecord.cpp (lines 187, 190)	Null pointer on sparkWallet	Added null check

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Note

Resolves crashes when sending/minting Spark by hardening wallet/Qt code and fixing a critical mempool check.

• Use the actual signed transaction (txNewConst) for mempool.IsTransactionAllowed in sparkwallet.cpp to avoid accessing an uninitialized wtx.tx
• Add null checks for pwalletMain->sparkWallet before accessing Spark data in wallet.cpp, transactionrecord.cpp, walletmodeltransaction.cpp, and sparkmodel.cpp
• Replace EnsureMintWalletAvailable() with EnsureSparkWalletAvailable() in Spark spend/name creation; add early null check in CreateSparkMintTransactions
• In sendcoinsdialog.cpp, call SendCoinsEntry::generateWarningText statically and update all SendCoinsEntry widgets when toggling anonymize mode

^{Written by Cursor Bugbot for commit f31778a. This will update automatically on new commits. Configure here.}

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch anonymize-spark-fix

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[reubenyap]

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