res:dock:: fix wrong input reigon.

dock gets wrong input region after dock is hidden.

reason:
'h = DOCK_HEIGHT unless h' on region.coffee, if h is 0, then h is assigned to
DOCK_HEIGHT.

solution:
h = DOCK_HEIGHT unless h?.

NOTE: add a flag named debugRegion to help debuging.

Change-Id: I5f8739c30cee94f620e2446cb9c2713478085102