protocol: allow to send a zero physical output size

Physical size doesn't always make sense for all outputs. In case
it's not available or not relevant, allow compositors to send zero.

Acked-by: Daniel Stone <>
Acked-by: Jonas Ådahl <>
Acked-by: Olivier Fourdan <>
1 job for master in 1 minute and 48 seconds (queued for 1 second)
Status Job ID Name Coverage
passed #11591