File chooser dialog hangs when a network bookmarks is unreachable.

The file chooser dialog hangs when a GTK bookmark points to a host that can be resolved but can't be reached.
This happens when an application invokes the method 'gtk_file_chooser_set_local_only' in order to request a backend that is not local.

What happens is that the application invoking the file dialog freezes and doesn't respond to events anymore until the dialog appears.
The problem is that the dialog takes a log time to appear.
During that time, the CPU usage, the load and the memory consumption are normal.
Everything seems to indicate that the application is waiting for something.
After a while, usually about 30 seconds, the file dialog appears and the application responds normally to events.

To reproduce the bug do the following:
1. Add a network bookmark to a host that can't be reached:
   echo "sftp://1.2.3.4/" >> ~/.gtk-bookmarks
2. Invoke a file dialog from an application, make sure that the gtk_file_chooser_set_local_only was invoked.
   For example, with gedit perform the following:
   File -> Open... 
3. Be patient and wait, eventually the file dialog will appear.

NOTE: In order to reproduce this bug it is important that the host used in the bookmark can be resolved. 
Use an IP address that can't be reached as the bookmark's host or add a hostname in the file /etc/hosts that resolves to an IP address that can't be reached and use that hostname.
If the bookmark has a hostname that can't be resolved the dialog will appear without any problems.