[SYSSETUP] Zero out propsheet data fields

This prevents +propsheet logging accessing uninitialized data

dll/win32/syssetup/wizard.c

@@ -2661,7 +2661,7 @@ typedef DWORD(WINAPI *PFNREQUESTWIZARDPAGES)(PDWORD, HPROPSHEETPAGE *, PSETUPDAT
 VOID
 InstallWizard(VOID)
 {
-    PROPSHEETHEADER psh;
+    PROPSHEETHEADER psh = {0};
     HPROPSHEETPAGE *phpage = NULL;
     PROPSHEETPAGE psp = {0};
     UINT nPages = 0;