Send monitor config if at least one monitor has dimensions
Send monitor config if at least one monitor has dimensions

If a client (virt-manager, spicy) is not setting display dimensions
and the "resize-guest" property is disabled, spice-gtk sends a wrong
monitor config message where all the monitors have width = heigh = 0
when the agent connects. This message can confuse the guest, in that
case the guest will change the resolution of its monitor.

Regression since 28312b8d1e287a320851e8828825f2ca138d8b0b

Resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=1240721

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