add an assertion


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@51645 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Rewrite/Rewriter.cpp b/lib/Rewrite/Rewriter.cpp
index bea7c00..e1a6651 100644
--- a/lib/Rewrite/Rewriter.cpp
+++ b/lib/Rewrite/Rewriter.cpp
@@ -100,6 +100,7 @@
 
 unsigned Rewriter::getLocationOffsetAndFileID(SourceLocation Loc,
                                               unsigned &FileID) const {
+  assert(Loc.isValid() && "Invalid location");
   std::pair<unsigned,unsigned> V = SourceMgr->getDecomposedFileLoc(Loc);
   FileID = V.first;
   return V.second;