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 <daniels@collabora.com>
Acked-by: Jonas Ådahl <jadahl@gmail.com>
Acked-by: Olivier Fourdan <ofourdan@redhat.com>

protocol/wayland.xml

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index b5662e0..141038b 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -2399,6 +2399,9 @@
 	The geometry event describes geometric properties of the output.
 	The event is sent when binding to the output object and whenever
 	any of the properties change.
+
+	The physical size can be set to zero if it doesn't make sense for this
+	output (e.g. for projectors or virtual outputs).
       </description>
       <arg name="x" type="int"
 	   summary="x position within the global compositor space"/>