LU-5635 llog: prevent out-of-bound index

LU-5635 llog: prevent out-of-bound index

llog_process_thread() can be called from llog_cat_process_cb with an
index already out of bound, leading to the following crash:

LustreError: 3773:0:(llog.c:310:llog_process_thread())
  ASSERTION(index <= last_index + 1 ) failed:
LustreError: 3773:0:(llog.c:310:llog_process_thread()) LBUG

 #0 [ffff8801144bf900] machine_kexec at ffffffff81038f3b
 #1 [ffff8801144bf960] crash_kexec at ffffffff810c5d82
 #2 [ffff8801144bfa30] panic at ffffffff8152798a
 #3 [ffff8801144bfab0] lbug_with_loc at ffffffffa02f8eeb [libcfs]
 #4 [ffff8801144bfad0] llog_process_thread at ffffffffa0413fff [obdclass]
 #5 [ffff8801144bfb80] llog_process_or_fork at ffffffffa041585f [obdclass]
 #6 [ffff8801144bfbd0] llog_cat_process_cb at ffffffffa0418612 [obdclass]
 #7 [ffff8801144bfc30] llog_process_thread at ffffffffa0413c22 [obdclass]
 #8 [ffff8801144bfce0] llog_process_or_fork at ffffffffa041585f [obdclass]
 #9 [ffff8801144bfd30] llog_cat_process_or_fork at ffffffffa0416b9d [obdclass]
    RIP: 00007f6de5e4f730  RSP: 00007fff9aa26d98  RFLAGS: 00000206
    RAX: 0000000000000000  RBX: ffffffff8100b072  RCX: 00007f6de5e4f730
    RDX: 0000000000008000  RSI: 00000000019c7000  RDI: 0000000000000003
    RBP: 00000000019c7000   R8: 00007f6de6103ee8   R9: 0000000000000001
    R10: 00007fff9aa26b20  R11: 0000000000000246  R12: ffffffffffff8000
    R13: 0000000000000003  R14: 0000000000008000  R15: 0000000000000003
    ORIG_RAX: 0000000000000000  CS: 0033  SS: 002b

If index is too big, simply return success.

Change-Id: I81bbedbbe2bcef478c370ef40fc069447d39efbd
Signed-off-by: frank zago <fzago@cray.com>
Reviewed-on: http://review.whamcloud.com/12161
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>