Minor cleanup to the code-completion-point logic suggested by Chris.

llvm-svn: 90459
diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index 8cc7a84..a3e72e8 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -47,8 +47,7 @@
 }
 
 void ContentCache::replaceBuffer(const llvm::MemoryBuffer *B) {
-  if (B == Buffer)
-    return;
+  assert(B != Buffer);
   
   delete Buffer;
   Buffer = B;