swift234

Fix implicit assumption that RetainArray is not nullptr.

The code in question was the following:

  auto *RetainArray = dyn_cast_or_null<StrongRetainInst>(getInstBefore(Call));
  if (!RetainArray && MayHaveBridgedObjectElementType)
    return false;
  auto *ReleaseArray = dyn_cast_or_null<StrongReleaseInst>(getInstAfter(Call));
  if (!ReleaseArray && MayHaveBridgedObjectElementType)
    return false;
  if (ReleaseArray &&
      ReleaseArray->getOperand() != RetainArray->getOperand())
    return false;

There is no check in the last if if RetainArray is not nullptr even though it is
possible for it to be so.

Found by clang static analyzer.