[OpenMP] Minor cleanup of debug code
[OpenMP] Minor cleanup of debug code

* Fix calculation of string length.
* Remove NULL-check of pointer which has been dereferenced.

Patch by Andrey Churbanov

Differential Revision: https://reviews.llvm.org/D54948


git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@347801 91177308-0d34-0410-b5e6-96231b3b80d8

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