Avoiding non necessary exceptions

As already said in previous issues, there are few exceptions that are raised for no reason (apparently).

I updated FastCharStream, QueryParserTokenManager, FieldInfos to avoid these kind of exception.

• FastCharStream.ReadChar() returns '\0' if we are trying to read byond the end of the stream.
• Updated QueryParserTokenManager to support the previous fix
• Update FieldInfos.FieldName. No more reading take place if fieldNumber is -1.