win32: free allocated gdi objects in 16bpp

In 16bpp, Gdk is creating hbitmap with CreateDIBSection() and a hdc with
CreateCompatibleDC(). Those 2 objects need to be released when the
pixmap is finalized.

https://bugzilla.gnome.org/show_bug.cgi?id=671538

Signed-off-by: Hans Breuer <hans@breuer.org>

gdk/win32/gdkpixmap-win32.c

@@ -125,6 +125,11 @@ gdk_pixmap_impl_win32_finalize (GObject *object)
 	  /* Drop our reference */
 	  cairo_surface_destroy (drawable_impl->cairo_surface);
 	  drawable_impl->cairo_surface = NULL;
+	  if (impl->is_allocated)
+	    {
+	      GDI_CALL (DeleteDC, (drawable_impl->hdc));
+	      GDI_CALL (DeleteObject, (GDK_PIXMAP_HBITMAP (wrapper)));
+	    }
 	}
     }
 
@@ -321,6 +326,7 @@ _gdk_pixmap_new (GdkDrawable *drawable,
 	}
 
       SelectObject (hdc, hbitmap);
+      pixmap_impl->is_allocated = TRUE;
     }
 
   /* We need to use the same hdc, because only one hdc

gdk/win32/gdkpixmap-win32.h

@@ -53,6 +53,7 @@ struct _GdkPixmapImplWin32
   gint height;
   guchar *bits;
   guint is_foreign : 1;
+  guint is_allocated : 1;
 };
  
 struct _GdkPixmapImplWin32Class