libgui: Copyback all region except dirty region for newly allocated buffer

Inside Surface::lock if new buffer is allocated
and DirtyRegion does not cover complete buffer
bounds then copyback may not cover all remaining area
as it copyback only area covered by dirty regions
from other buffers. This will lead to left out
black area which may cause flicker.

Change-Id: I4a3f7a56fc5fbaf4af926584919577d8d34bed57