gvfs freeze break request

[Alexander Larsson <alexl redhat com>]

You're gonna hate me, but i have another gvfs sftp fix:

Basically, if ssh exits early during login because there are no more
authentication methods availible we get stuck looping using 100% cpu.

Fix is easy, just detect reads of 0 bytes which mean end of file.

Bug: http://bugzilla.gnome.org/show_bug.cgi?id=574754
Patch: http://bugzilla.gnome.org/attachment.cgi?id=130400&action=view