ui: fix zero-sized panels on fresh chrome start

ui: fix zero-sized panels on fresh chrome start

it seems in new versions of chrome , this triggers too early on a fresh
start (when autostarting a pve tab), resulting in the
'viewWidth'/'viewHeight' being zero pixels. This means we set the width
of the left and the height of the bottom panel to zero pixels, making
them functionally invisible.

To prevent that, check that the 'viewWidth'/'viewHeight' is big enough
so that the panels still have least 50 pixels left before setting their
size.

Reported in the Forum:
https://forum.proxmox.com/threads/136636/

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
 [ TL: point to forum thread ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>