[NtRegistry] Ensure REG_SZ and REG_MULTI_SZ are null terminated.

Enforced in base QueryRegKeyValue function.

TBR=robertshield
BUG=714401
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win10_chromium_x64_rel_ng

Review-Url: https://codereview.chromium.org/2885243002
Cr-Commit-Position: refs/heads/master@{#490780}
3 files changed