make PTH not crash on a null directive (# on its own line)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69523 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/clang-cc/CacheTokens.cpp b/tools/clang-cc/CacheTokens.cpp
index 6e2a20d..c417eb4 100644
--- a/tools/clang-cc/CacheTokens.cpp
+++ b/tools/clang-cc/CacheTokens.cpp
@@ -475,8 +475,10 @@
 
       // Get the next token.
       L.LexFromRawLexer(Tok);
-            
-      assert(!Tok.isAtStartOfLine());
+
+      // If we see the start of line, then we had a null directive "#".
+      if (Tok.isAtStartOfLine())
+        goto NextToken;
       
       // Did we see 'include'/'import'/'include_next'?
       if (Tok.isNot(tok::identifier)) {