fix combobox reset behaviour

fix combobox reset behaviour

on comboboxes/combogrids with multiselect,
if you deselect an item (but not the last),
the order of the selected items after resetting is
not the same as the original order

because of this, the reset button is still enabled

this happens, because extjs only adds the missing
values instead of overwriting the whole array

with this fix, we overwrite the reset function of
the comboboxes and only if the values do not match
(after a reset) do we clear and set the value again

so we only change the behaviour when it is necessary

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