Avoid capture all black screenshot bitmap

Captured screenshot bitmap is all black one if none of windows is
surface shown.

Change-Id: I651b2ade1865926d61f945167d60219535fa8bf8
Signed-off-by: tingna_sung <tingna_sung@htc.com>

(cherry picked from commit 1b003152065f689cebb4d0a31a3fc64b2c82015a)