[libclang] Don't crash when saving a PCH from a prefix header
that does not exist.

rdar://11607033

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158193 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index a508b77..8eaf4ec 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -2692,6 +2692,8 @@
 
   ASTUnit *CXXUnit = static_cast<ASTUnit *>(TU->TUData);
   ASTUnit::ConcurrencyCheck Check(*CXXUnit);
+  if (!CXXUnit->hasSema())
+    return CXSaveError_InvalidTU;
 
   SaveTranslationUnitInfo STUI = { TU, FileName, options, CXSaveError_None };