[Tail] Tail input does not work with built-in multiline + Path_Key

[BinaryFissionGames]

Bug Report

Describe the bug
When specifying both a multiline config (multiline.parser) and Path_Key in the config, fluent-bit drops all log messages with this message:

[2022/10/19 15:05:47] [debug] [input chunk] skip ingesting data with 0 bytes

To Reproduce
fluent_bit_main.conf:

[INPUT]
    Name              tail
    Key               message
    Path              ./test.log
    Path_Key          path
    Read_from_Head    True
    Tag               json_log
    multiline.parser  multiline_parser

[OUTPUT]
    Match *
    Name stdout

fluent_bit_parser.conf:

[MULTILINE_PARSER]
    flush_timeout 5000
    name          multiline_parser
    type          regex
    rule          "start_state"    "^{.*"    "cont"
    rule          "cont"    "^[^{]"    "cont"

test.log:

{"message": "test_message"}
{"message": "test_message2"}
{
 "message": "multi-line-message"
}

Run with:

/opt/fluent-bit/bin/fluent-bit --config fluent_bit_main.conf --parser fluent_bit_parser.conf --verbose

Expected behavior
Three log mesages are output to stdout; Currently, none are put out, and

[2022/10/19 15:05:47] [debug] [input chunk] skip ingesting data with 0 bytes

is put into stdout.

If I remove either the multiline or Path_Key config options, log messages are spit out in the manner expected (e.g. no multiline, or no Path_Key).

Your Environment

• Version used: 1.9.9 (installed through package manager)
• Operating System and version: Debian 11 (bullseye)

Related issues:

• [Tail] Can't tail symlink file when set Path_Key #5964
• built in mulitline parser breaks tail input in versions 1.8.12 and newer #5323