Fix failures caused by r12598.

R=verwaest@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/10958070

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12599 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/json-parser.h

@@ -577,6 +577,7 @@ Handle<String> JsonParser<seq_ascii>::ScanJsonString() {
                                                         position_,
                                                         position);
       }
+      if (c0_ < 0x20) return Handle<String>::null();
       running_hash = StringHasher::AddCharacterCore(running_hash, c0);
       position++;
       if (position > source_length_) return Handle<String>::null();