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
(cherry picked from commit a7e07d2ab6953ea616f52faf92843a1d70febf20)
Merge "Keyguard: HU translation" into cm-11.0
(cherry picked from commit 1a19c932e2ca88af456b60e57182263b2cf50413)
Merge "FrameworkBase/KeyGuard: CS translation" into cm-11.0
(cherry picked from commit 87ec462b6723f803785ceda05ae9eaf660d9bd3c)