Initialize pointer members to NULL to avoid illegal reference

mBitmap and mTexture is not initialized to NULL which causes
illegal address access when it fails to be created from
oversized bitmap.
Cherry-picked from AOSP: https://android-review.googlesource.com/#/c/79320/

Change-Id: Iea54bec8788bc5f3a10040fdb43f416c0d41a14c