Fix crasher when checking for "of", but next token has no literal buffer

src/scanner.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 313 matching lines @@
   }
   Vector<const uc16> literal_utf16_string() {
     ASSERT_NOT_NULL(current_.literal_chars);
     return current_.literal_chars->utf16_literal();
   }
   bool is_literal_ascii() {
     ASSERT_NOT_NULL(current_.literal_chars);
     return current_.literal_chars->is_ascii();
   }
   bool is_literal_contextual_keyword(Vector<const char> keyword) {
-    ASSERT_NOT_NULL(next_.literal_chars);
+    ASSERT_NOT_NULL(current_.literal_chars);
     return current_.literal_chars->is_contextual_keyword(keyword);
   }
   int literal_length() const {
     ASSERT_NOT_NULL(current_.literal_chars);
     return current_.literal_chars->length();
   }
 
   bool literal_contains_escapes() const {
     Location location = current_.location;
     int source_length = (location.end_pos - location.beg_pos);
@@ skipping 210 matching lines @@
   bool has_multiline_comment_before_next_;
   // Whether we scan 'let' as a keyword for harmony block-scoped let bindings.
   bool harmony_scoping_;
   // Whether we scan 'module', 'import', 'export' as keywords.
   bool harmony_modules_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_H_