Windows: Validate any user handle permissions for syscall callbacks

In the terminate case, if we don't return early then we will delete the
FEX thread object but the actual terminate call that follows will
fail, leaving the thread in a bad state.

Source/Windows/include/winternl.h

@@ -537,7 +537,7 @@ NTSTATUS WINAPI RtlWow64GetThreadContext(HANDLE, WOW64_CONTEXT*);
 NTSTATUS WINAPI RtlWow64SetThreadContext(HANDLE, const WOW64_CONTEXT*);
 void WINAPI Wow64ProcessPendingCrossProcessItems(void);
 NTSTATUS WINAPI Wow64SystemServiceEx(UINT, UINT*);
-NTSTATUS WINAPI RtlWow64SuspendThread(HANDLE,ULONG*);
+NTSTATUS WINAPI RtlWow64SuspendThread(HANDLE, ULONG*);
 
 #ifdef __cplusplus
 }