performance/write-behind: Add a NULL check for request->stub before checking request->stub->fop.

- for non-write wind requests, the request structure outlives the stub.
    The call stub is destroyed when stack is wound but request is destroyed
    only when the reply has come.
    (for writes, both stub and request are destroyed when refcount becomes 0,
     which happens only when the write operation is stack unwound and a reply
     for the write operation has come from underlying translators, for non-write
     unwind requests the request is first destroyed before resuming the stub).

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

BUG: 280 (simple stripe, with write-behind set up, when dbench is run client crashes.)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=280

0 files changed, 0 insertions, 0 deletions