[Object, COFF] An import data directory might not consist soley of imports

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
3 files changed