Fix ntdll!RtlFreeHeap freeze: correct WM_INITDIALOG lParam extraction for property sheet pages

[Copilot]

In MSYS2 builds, opening General Settings froze in ntdll!RtlFreeHeap because three dialog procs used as property sheet pfnDlgProc misinterpreted the WM_INITDIALOG lParam.

Root cause

When a dialog proc is used as a property sheet page's pfnDlgProc, Windows passes a PROPSHEETPAGEW* as lParam in WM_INITDIALOG — not the value stored in psp.lParam. The three affected procs cast lParam directly to their dialog class pointer:

// In XG_SettingsDialog::DialogProc, XG_RulePresetDialog::DialogProc, XG_HiddenDialog::DialogProc
s_pThis = (XG_SettingsDialog*)lParam;  // lParam is PROPSHEETPAGEW*, not &dialog1
SetWindowLongPtrW(hwnd, DWLP_USER, (LONG_PTR)lParam);

Subsequent member-variable writes (e.g. m_lfCellFont = xg_lfCellLogFont, m_bUpdating = TRUE) then stomped the comctl32-allocated PROPSHEETPAGEW heap block — overwriting dwSize, dwFlags, hInstance. When PropertySheetW tore down the pages, the corrupted block caused RtlFreeHeap to hang.

Fix

Added three thin wrapper procs in GUI.cpp (just before XgGeneralSettings) that intercept WM_INITDIALOG, replace lParam with the correct value from PROPSHEETPAGEW::lParam, then forward to the existing DialogProc:

static INT_PTR CALLBACK XgSettingsPageProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    if (uMsg == WM_INITDIALOG)
        lParam = reinterpret_cast<PROPSHEETPAGEW*>(lParam)->lParam;
    return XG_SettingsDialog::DialogProc(hwnd, uMsg, wParam, lParam);
}
// XgRulePresetPageProc and XgHiddenPageProc are identical in structure

XgGeneralSettings now sets psp.pfnDlgProc to these wrappers instead of the class DialogProc directly. The DoModal paths and the original DialogProc implementations are untouched.