grn_ts: initialize a variable to suppress warnings
grn_ts: initialize a variable to suppress warnings

The warnings are as follows:
/home/buildbot/buildbot/build/storage/mroonga/vendor/groonga/lib/ts.c:7569:
 warning: ‘token.ptr’ may be used uninitialized in this function
/home/buildbot/buildbot/build/storage/mroonga/vendor/groonga/lib/ts.c:7569:
 warning: ‘token.size’ may be used uninitialized in this function

naoa/groonga,komainu8/groonga,naoa/groonga,groonga/groonga,kenhys/groonga,cosmo0920/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,cosmo0920/groonga,groonga/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,komainu8/groonga,groonga/groonga,cosmo0920/groonga,groonga/groonga,cosmo0920/groonga,groonga/groonga,naoa/groonga,cosmo0920/groonga,naoa/groonga,kenhys/groonga,naoa/groonga,komainu8/groonga,cosmo0920/groonga,komainu8/groonga,naoa/groonga,kenhys/groonga,cosmo0920/groonga,naoa/groonga,cosmo0920/groonga,komainu8/groonga,komainu8/groonga,komainu8/groonga,kenhys/groonga,kenhys/groonga,komainu8/groonga,groonga/groonga