Suppress a warning
Suppress a warning

    ha_mroonga.cpp: In member function 'int ha_mroonga::drop_index(MRN_SHARE*, uint)':
    ha_mroonga.cpp:8595:26: warning: 'target_name_length' may be used uninitialized in this function [-Wmaybe-uninitialized]
                  ctx->errbuf);
                              ^

mroonga/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga,mroonga/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,yoku0825/mroonga,mroonga/mroonga