Block dotless-i / j + a combining mark

U+0131 (doltess i) and U+0237 (dotless j) are blocked from being
followed by a combining mark in U+0300 block.

Bug: 774842
Test: See the bug
Change-Id: I92aac0e97233184864d060fd0f137a90b042c679
Reviewed-on: https://chromium-review.googlesource.com/767888
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517605}