afr: fix crash in afr_sh_data_close
afr: fix crash in afr_sh_data_close

when active_sink count is 0, the code proceeded into a dangerous loop
resulting in a crash while issuing the call or in the callback
afr_sh_data_setattr_cbk or afr_sh_data_flush_cbk

Signed-off-by: Anand V. Avati <avati@blackhole.gluster.com>
Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 170 (Auto-heal fails on files that are open()-ed/mmap()-ed)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=170

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster