[leaks] Re-shuffle code such that we don't create a basic block for
initializing an array unless we need it. Specifically, position the
creation of a new basic block after we've checked all of the cases that
bypass the need for it.

Fixes another leak in test/CodeGen* found by LSan.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207900 91177308-0d34-0410-b5e6-96231b3b80d8