Fix lock leak in be_pair_flush() if flush type is BEV_NORMAL Fixes: bufferevent/bufferevent_pair_flush_normal $ regress --no-fork bufferevent/bufferevent_pair_flush_normal bufferevent/bufferevent_pair_flush_normal: FAIL ../test/regress_bufferevent.c:181: assert(bufferevent_pair_get_partner(bev1) == NULL): 0x177fa20 vs (nil) [bufferevent_pair_flush_normal FAILED] Fixes #266