LU-9076 ptlrpc: Prevent possible dereference of NULL pointers

LU-9076 ptlrpc: Prevent possible dereference of NULL pointers

Check pointers for NULL before passing to other functions.

Signed-off-by: Steve Guminski <stephenx.guminski@intel.com>
Change-Id: I5ad1e6675e9c5e41aee2dc59045ed67e9da5ea0d
Reviewed-on: https://review.whamcloud.com/25909
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>