fix drag&drop for pointerType 'pen'

fix drag&drop for pointerType 'pen'

some devices (e.g. vms via novnc, and some laptops) get the pointerType
'pen' under chromium.

the DragZone handler tries to ignore touch input for that by
checking for "=== 'mouse'" which does not include 'pen'
so override that to handle it when the pointerType !== 'touch'

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>