Keyboard does not scale when display->allocation.width/height == 0
This breaks scaling the on screen keyboard in our QEMU VM:
if (output->allocation.width == 0 && output->allocation.height == 0) continue;
however e.g. custom modes in QXL have no approprite size information (which can also happen with broken edid):
$ weston-info … interface: 'wl_output', version: 3, name: 20 x: 0, y: 0, scale: 2, physical_width: 0 mm, physical_height: 0 mm, make: '<Unknown>', model: '<Unknown>',
so this should be handled properly.