input: Fix crash when touchscreen generates out of screen coordinate

input: Fix crash when touchscreen generates out of screen coordinate

With change 61ed7b6b, global touch coordinates are being passed to the
touch grab.  However, touch->grab is undefined in certain circumstances
such as when the touch screen raises an axis X value larger than the
maximum expected.  Move the check for this condition earlier, before our
first use of the pointer.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=92736

Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>