Fix a bug when we fail to find the data format in a BOV.
Fix a bug when we fail to find the data format in a BOV.

If we didn't find a format, the pointer would be unset yet we'd
compare it to NULL.  This initializes the pointer to NULL,
ensuring we don't read uninitialized memory.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1040 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok