This fixes warning on android_arm build.
Previously the compiler complained about a check that can never be true.
See second check below(index is size_t type, FIRST_SPACE=0):
if (index > i::LAST_SPACE || index < i::FIRST_SPACE)
And make the code easy to understand.

BUG=

Review URL: https://codereview.chromium.org/1155043005

Cr-Commit-Position: refs/heads/master@{#29042}