Fix a crash in our error reporting

AF = dyn_cast<SCEVAddRecExpr>(Pair.second) may be NULL for some SCEVs that we do
not support. When reporting the error we still want to pass a pointer that is
known to always be non-NULL.

I do not yet have a test case for this, unfortunately.

llvm-svn: 225461
diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index ee7ed9b..1bfd969 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -457,8 +457,8 @@
       if (IsNonAffine) {
         BasePtrHasNonAffine = true;
         if (!AllowNonAffine)
-          invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, AF, Insn,
-                                         BaseValue);
+          invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, Pair.second,
+                                         Insn, BaseValue);
         if (!KeepGoing && !AllowNonAffine)
           return false;
       }