libhwui: fix texture memory leak

When there is not enough space and we cannot delete any
Texture in TextureCache to secure space, a new Texture is
created over and over again for the same SkBitmap and
there is the case that it is not deleted.
This patch avoids such cases.

Change-Id: Ic5353995e6d0716c31fe3bb49c60ec1a71574643
Signed-off-by: Dohyun Lee <leedhyun11@gmail.com>