Clarify an assert.

llvm-svn: 100776
diff --git a/clang/lib/CodeGen/CGVtable.cpp b/clang/lib/CodeGen/CGVtable.cpp
index e23289a..c157a5e 100644
--- a/clang/lib/CodeGen/CGVtable.cpp
+++ b/clang/lib/CodeGen/CGVtable.cpp
@@ -2544,6 +2544,9 @@
 
 uint64_t
 CodeGenVTables::getAddressPoint(BaseSubobject Base, const CXXRecordDecl *RD) {
+  assert(AddressPoints.count(std::make_pair(RD, Base)) &&
+         "Did not find address point!");
+
   uint64_t AddressPoint = AddressPoints.lookup(std::make_pair(RD, Base));
   assert(AddressPoint && "Address point must not be zero!");