Handle fatal error on exception in __toString methods

[antonsergeyev]

When a NormalizerFormatter tries to normalize an object that implements '__toString' method, and this method throws an exception (which is exceptionally bad, but still), it results in a messy fatal error, which is hard to debug. This is especially painful if happens in the process of logging another error or exception, so we end up not knowing what the original error was.

The solution, i think, is to simply call '$data->__toString()' instead of '(string) $data', which will correctly throw an exception instead of triggering fatal error.