Attributor: Don't crash on indirect calls in AAInvariantLoadPointer (#231519)
AAInvariantLoadPointerCallSiteReturned assumed every call has a known
callee, and dereferenced the missing function of an indirect call. This
crashed on most of CTMark with -attributor-enable=full. Nothing is known
about the result of an indirect call, so give up on it.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>