socket: ignore packet if FIONREAD returns zero
socket: ignore packet if FIONREAD returns zero

zero size is reported for corrupt packets. recvmsg() later could
nevertheless get data from a good packet that followed the bad one.
So get out early to avoid hitting an assertion.

heftig/avahi-1,gloryleague/avahi,lathiat/avahi,heftig/avahi,catta-x/catta,heftig/avahi-1,gloryleague/avahi,heftig/avahi,Kisensum/xmDNS-avahi,heftig/avahi-1,lathiat/avahi,heftig/avahi,heftig/avahi-1,Distrotech/avahi,everbase/catta,lathiat/avahi,Kisensum/xmDNS-avahi,everbase/catta,gloryleague/avahi,Distrotech/avahi,gloryleague/avahi,Kisensum/xmDNS-avahi,Distrotech/avahi,Kisensum/xmDNS-avahi,lathiat/avahi,Kisensum/xmDNS-avahi,lathiat/avahi,heftig/avahi-1,catta-x/catta,Distrotech/avahi,gloryleague/avahi,gloryleague/avahi,Distrotech/avahi,heftig/avahi,lathiat/avahi,everbase/catta,heftig/avahi,Kisensum/xmDNS-avahi,Distrotech/avahi,heftig/avahi,heftig/avahi-1,catta-x/catta