background: Fix crasher when entering/leaving the background panel

g_application_get_dbus_connection() does not return a ref, so we
shouldn't try to free it.
network: Don't include spaces in proxy's ignore-hosts setting

We should also ignore any zero length strings resulting from
g_strsplit_set().

https://bugzilla.gnome.org/show_bug.cgi?id=707966
network: Fix empty ignore-hosts setting

If the ignore-hosts setting is set to an empty array we were using
unintialized memory.

This also now ignores zero length strings if there are any in the
array.

https://bugzilla.gnome.org/show_bug.cgi?id=707966