[glibmm] Glib::Dispatcher: Don't cast a HANDLE to an int on Windows

[Kjell Ahlstedt <kjellahl src gnome org>]

commit da9c5f725335b7b819a3909faff5bd53bdec4299
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Tue Dec 6 16:41:14 2016 +0100

    Glib::Dispatcher: Don't cast a HANDLE to an int on Windows
    
    * glib/glibmm/dispatcher.cc: When a Windows HANDLE must be cast, cast it
    to Glib::PollFD::fd_t instead of int. Bug 772074

 glib/glibmm/dispatcher.cc |   12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)
---
diff --git a/glib/glibmm/dispatcher.cc b/glib/glibmm/dispatcher.cc
index 3c8a65d..73b69be 100644
--- a/glib/glibmm/dispatcher.cc
+++ b/glib/glibmm/dispatcher.cc
@@ -165,8 +165,6 @@ private:
 
 /**** Glib::DispatchNotifier ***********************************************/
 
-// static
-
 thread_local DispatchNotifier* DispatchNotifier::thread_specific_instance_ = nullptr;
 
 DispatchNotifier::DispatchNotifier(const Glib::RefPtr<MainContext>& context)
@@ -186,11 +184,11 @@ DispatchNotifier::DispatchNotifier(const Glib::RefPtr<MainContext>& context)
 
   try
   {
-#ifdef G_OS_WIN32
-    const int fd = GPOINTER_TO_INT(fd_receiver_);
-#else
-    const int fd = fd_receiver_;
-#endif
+    // PollFD::fd_t is the type of GPollFD::fd.
+    // In Windows, it has the same size as HANDLE, but it's not guaranteed to be the same type.
+    // In Unix, a file descriptor is an int.
+    const auto fd = (PollFD::fd_t)fd_receiver_;
+
     // The following code is equivalent to
     // context_->signal_io().connect(
     //   sigc::mem_fun(*this, &DispatchNotifier::pipe_io_handler), fd, Glib::IO_IN);