[GHC] #9026: [CID43163, CID43172] Use correct variable in NULL-check

[GHC]

#9026: [CID43163, CID43172] Use correct variable in NULL-check
------------------------------------+-------------------------------------
       Reporter:  nicolast          |             Owner:  simonmar
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Runtime System    |           Version:  7.8.2
       Keywords:  coverity          |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
------------------------------------+-------------------------------------
 I *think* the attached patch fixes the issue reported by Coverity as
 CID43163, which then fixes CID43172 as a side-effect as well.

 Please give this a close look.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9026>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler