Assume UniqueID is zero for invalid PPRegion to fix uninitialized reads reported by MSan

llvm-svn: 187647
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index e2b898b..48fd43b 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -92,7 +92,7 @@
   time_t ModTime;
   unsigned Offset;
 public:
-  PPRegion() : ModTime(), Offset() {}
+  PPRegion() : UniqueID(0, 0), ModTime(), Offset() {}
   PPRegion(llvm::sys::fs::UniqueID UniqueID, unsigned offset, time_t modTime)
       : UniqueID(UniqueID), ModTime(modTime), Offset(offset) {}