[UDFS] Fix async paging IO wait handling without boolean literals

[Copilot]

Paging IO code paths in read.cpp and write.cpp could incorrectly return STATUS_CANT_WAIT or deadlock when Wait was FALSE on entry for an async paging IO request. The fix mirrors the canonical Windows FS driver pattern of setting IRP_CONTEXT_FLAG_WAIT on the IrpContext and deriving Wait from it, rather than assigning a boolean literal.

Changes

• read.cpp: Added missing async paging IO guard before _SEH2_TRY — absent entirely before this change, meaning Wait could remain FALSE through the if (!Wait) guard in the non-cached read path.
• write.cpp: Replaced Wait = TRUE in the existing paging IO guard with SetFlag + BooleanFlagOn, consistent with how Wait is initialized from IrpContext->Flags at function entry.

// Before (write.cpp):
if (!Wait && PagingIo) {
    Wait = TRUE;
    SetFlag(IrpContext->Flags, IRP_CONTEXT_FLAG_WAIT);
}

// After (both read.cpp and write.cpp):
if (!Wait && PagingIo) {
    SetFlag(IrpContext->Flags, IRP_CONTEXT_FLAG_WAIT);
    Wait = BooleanFlagOn(IrpContext->Flags, IRP_CONTEXT_FLAG_WAIT);
}

SetFlag is the authoritative mutation; Wait is kept in sync by re-deriving it from the flag, matching the existing initialization pattern at line 125 (read.cpp) and line 79 (write.cpp).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[UDFS] Find a way to do what the linked PR does without using a boolean</issue_title>
<issue_description>Find a way to do what the PR at assorted#2 does without using a boolean.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [UDFS] Find a way to do what the linked PR does without using a boolean #72

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.