wayland: Ensure the touch sequence pointer value is non-null
wayland: Ensure the touch sequence pointer value is non-null

Weston numbers its touch sequences ids starting from 0, thus simply
setting the GtkEvents touch.sequence to the touch id value typically
causes gdk_event_get_event_sequence to return NULL. Unfortunately this
confuses other parts of GDK.

As both weston & mutter keep the sequence id between 0..max_dev_touches
-1 simply use + 1 to keep the id > 0. While this isn't entirely correct
(compositor could send -1 as the touch id), this keeps the touch id in
gtk tied to the touch id from weston which is useful for debugging. A
more thorough solution could be done when it turns out this is an issue
in practise

https://bugzilla.gnome.org/show_bug.cgi?id=731371

jadahl/gtk,Lyude/gtk-,Lyude/gtk-,Lyude/gtk-,jessevdk/gtk,davidgumberg/gtk,jadahl/gtk,jessevdk/gtk,grubersjoe/adwaita,grubersjoe/adwaita,Lyude/gtk-,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,jessevdk/gtk,chergert/gtk,chergert/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk,ahodesuka/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,jadahl/gtk,jessevdk/gtk,davidgumberg/gtk,ahodesuka/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,ahodesuka/gtk,Lyude/gtk-,jadahl/gtk,jessevdk/gtk,jigpu/gtk,ahodesuka/gtk,Lyude/gtk-,jadahl/gtk,chergert/gtk,jigpu/gtk,ahodesuka/gtk,Adamovskiy/gtk,davidgumberg/gtk,Lyude/gtk-,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,jessevdk/gtk,Adamovskiy/gtk,jessevdk/gtk,chergert/gtk,grubersjoe/adwaita,alexlarsson/gtk,Lyude/gtk-,jadahl/gtk,Adamovskiy/gtk,jigpu/gtk,ahodesuka/gtk,davidgumberg/gtk,ahodesuka/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,chergert/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,ahodesuka/gtk,Adamovskiy/gtk