PinyinIME: Properly cast a boolean

Summary:
false is of bool type, but passes a jboolean pointer in this case.
We can cast it the same as the argument it's expected to pass to fix
the build with clang.

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D101