JSON_PARSER.parse_string can exhaust memory #160
Description
If an incomplete JSON document is being parsed (e.g. if you have only fetched 8K out of a 380K HTTP response), then parse_string will keep appending NULLs to the end of the string until memory is exhausted. This is because it keeps calling next without then testing if we have passed the end of the data, and actual returns %U.
It should check if we have passed the end of the data and set has_more to True (and is_parsed to False).