The last import is the penultimate entry, the last entry is nulled out.
Data beyond the null entry should not be considered to hold import
entries.
This fixes PR28302.
N.B. I am working on a reduced testcase, the one in PR28302 is too
large.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273790 91177308-0d34-0410-b5e6-96231b3b80d8