[NFC] Initialize a variable to prevent future invalid deref.

[NFC] Initialize a variable to prevent future invalid deref.

Found by KlockWorks, this variable is properly protected, however
the conditions in the test that initializes it and the one that uses
it could diverge, it seems to me that this is a 'free' init that will
prevent issues if one of the conditions is ever modified without the other.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@338909 91177308-0d34-0410-b5e6-96231b3b80d8