CIndex: initialise TU

TU is not guaranteed to be initialised in all cases.  In particular if CIdx or
ast_filename is NULL (or if &TU is NULL), then clang_createTranslationUnit2 will
not initialise the out parameter out_TU.  This is followed by an assertion check
which may perform a branch based on unitialised memory.

Caught by scan-build.

llvm-svn: 201628

clang/tools/libclang/CIndex.cpp

@@ -2612,7 +2612,7 @@ void clang_toggleCrashRecovery(unsigned isEnabled) {
 
 CXTranslationUnit clang_createTranslationUnit(CXIndex CIdx,
                                               const char *ast_filename) {
-  CXTranslationUnit TU;
+  CXTranslationUnit TU = NULL;
   enum CXErrorCode Result =
       clang_createTranslationUnit2(CIdx, ast_filename, &TU);
   (void)Result;