Fix crash when IntervalMapOverlaps::advanceTo moves past the last overlap.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122081 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/ADT/IntervalMapTest.cpp b/unittests/ADT/IntervalMapTest.cpp
index e0d95a1..eb1f1a4 100644
--- a/unittests/ADT/IntervalMapTest.cpp
+++ b/unittests/ADT/IntervalMapTest.cpp
@@ -586,7 +586,11 @@
   ASSERT_TRUE(BA.valid());
   EXPECT_EQ(3u, BA.a().start());
   EXPECT_EQ(4u, BA.b().start());
-  ++BA;
+  // advance past end.
+  BA.advanceTo(6);
+  EXPECT_FALSE(BA.valid());
+  // advance an invalid iterator.
+  BA.advanceTo(7);
   EXPECT_FALSE(BA.valid());
 }