[clang-format] fix crash involving invalid preprocessor line

Summary:
This (invalid) fragment is crashing clang-format:
```
#if 1
int x;
#elif
int y;
#endif
```

The reason being that the parser expects a token after `#elif`, and the
subsequent parsing of the next line does not check if `CurrentToken` is null.

Reviewers: gribozavr

Reviewed By: gribozavr

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65940

llvm-svn: 368280

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 6e0369f27e7..cc0a954dbfb 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -1099,6 +1099,8 @@ private:
 
 public:
   LineType parseLine() {
+    if (!CurrentToken)
+      return LT_Invalid;
     NonTemplateLess.clear();
     if (CurrentToken->is(tok::hash))
       return parsePreprocessorDirective();