GDK W32: fix monitor pruning code

Decrement the counter for each removed element, otherwise we skip
one element every time we remove one. Also, no need for continue here.

gdk/win32/gdkmonitor-win32.c

@@ -766,10 +766,7 @@ prune_monitors (EnumMonitorData *data)
       m = g_ptr_array_index (data->monitors, i);
 
       if (m->remove)
-        {
-          g_ptr_array_remove_index (data->monitors, i);
-          continue;
-        }
+        g_ptr_array_remove_index (data->monitors, i--);
     }
 }