afp: Change g_error to g_warning for read errors
afp: Change g_error to g_warning for read errors

Use g_warning rather than g_error when a read error occurs to prevent
spurious crash reports since there are many different ways for a read
from the network to fail.

[Cherry-picked from gnome-3-14/14369db2a8fc
 Commit message written by Ross Lagerwall.]

https://bugzilla.gnome.org/show_bug.cgi?id=710490

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs