external/clucene: Avoid InitOrderFiasco

...as reported by AddressSanitizer, where src/core/CLucene/index/IndexWriter.cpp
initializes IndexWriter::MAX_TERM_LENGTH with the value of
DocumentsWriter::MAX_TERM_LENGTH before the latter is initialized in
src/core/CLucene/index/DocumentsWriter.cpp.  But turns out that
IndexWriter::MAX_TERM_LENGTH is completely unused.

Change-Id: Ica01186584ec05a989a13dc58823f4751e8724e2