channel: check too long password
channel: check too long password

Make sure that the password length is under the maximum lenght. If not
report it as an authentication failure with an adapted message.

fgouget/spice-gtk,SPICE/spice-gtk,flexVDI/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk