Don't pad before calling writeInPlace().

writeInplace() itself already pads securely, by masking off
the padded bytes. If the padding is done before calling
writeInplace(), no mask is applied, and heap data can leak.

Bug: 77237570
Test: builds
Change-Id: Ide27a0002d4ed4196530430760245b971f6a3f44
Merged-In: Ide27a0002d4ed4196530430760245b971f6a3f44

(cherry picked from commit f8542381)
(cherry picked from commit 732132b7)

Change-Id: Id65e4573e18ab68b804f1cf63a6977a71da01e5d
CVE-2018-9421