Severe: malformed JSON

Sometimes server reports Severe: JsonSyntaxException.

There are two main reason of the issue: part of xml/html instead of json and concatenation of two jsons:

```
SEVERE: !{"method_name":"updated?","call_info_argc":"-1","call_info_kw_args":"","args_info":"","visibility":"PUBLIC","path":"/Users/vkkoshelev/work/rails/activesupport/lib/active_support/file_update_checker.rb","lineno":"61","receiver_name":"ActiveSupport::FileUpdateChecker","return_type_name":"FalseClass","gem_name":"","gem_version":""}{"method_name":"multiline?","call_info_argc":"-1","call_info_kw_args":"","args_info":"","visibility":"PUBLIC","path":"/Users/vkkoshelev/work/rails/activesupport/lib/active_support/core_ext/regexp.rb","lineno":"4","receiver_name":"Regexp","return_type_name":"FalseClass","gem_name":"","gem_version":""}!
com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 332 path $
```