filter_modify: fix clean up function for cond/rule(#7368)

[nokute78]

Fixes #7368

This patch is to

• Add rule_free to release struct modify_rule
• Check if valid pointer before releasing
• Use flb_calloc to initialize members of struct
• Add test code for Segv from simple wildcard #7368

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Run local packaging test showing all targets (including any new ones) build.
• [N/A] Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• [N/A] Documentation required for this feature

Backporting

• Backport to latest stable release.

Configuration

[SERVICE]
    Flush      1
    Grace      2
    Log_Level  info

[INPUT]
    Name       dummy
    Dummy      {"r1":"someval"}
    Samples    1

[FILTER]
    Name                 modify
    Match                *
    Log_Level            debug
    Remove_wildcard      *s3

[OUTPUT]
    Name  stdout
    Match *

[OUTPUT]
    Name exit
    Match *

Debug/Valgrind output

$ valgrind --leak-check=full bin/flb-rt-filter_modify 
==34097== Memcheck, a memory error detector
==34097== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==34097== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==34097== Command: bin/flb-rt-filter_modify
==34097== 
Test op_set_append...                           [2023/05/13 08:13:56] [ info] [fluent bit] version=2.1.3, commit=4398840ed5, pid=34097
[2023/05/13 08:13:57] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/05/13 08:13:57] [ info] [cmetrics] version=0.6.1

(snip)

Test invalid_wildcard...                        [2023/05/13 08:15:10] [ info] [fluent bit] version=2.1.3, commit=4398840ed5, pid=34097
[2023/05/13 08:15:10] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/05/13 08:15:10] [ info] [cmetrics] version=0.6.1
[2023/05/13 08:15:10] [ info] [ctraces ] version=0.3.0
[2023/05/13 08:15:10] [ info] [input:lib:lib.0] initializing
[2023/05/13 08:15:10] [ info] [input:lib:lib.0] storage_strategy='memory' (memory only)
[2023/05/13 08:15:10] [error] [filter:modify:modify.0] Unable to create regex(key) from *s3
[2023/05/13 08:15:10] [error] Failed initialize filter modify.0
[2023/05/13 08:15:10] [error] [engine] filter initialization failed
[2023/05/13 08:15:10] [error] [lib] backend failed
[ OK ]
SUCCESS: All unit tests have passed.
==34097== 
==34097== HEAP SUMMARY:
==34097==     in use at exit: 0 bytes in 0 blocks
==34097==   total heap usage: 56,139 allocs, 56,139 frees, 28,221,757 bytes allocated
==34097== 
==34097== All heap blocks were freed -- no leaks are possible
==34097== 
==34097== For lists of detected and suppressed errors, rerun with: -s
==34097== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[leonardo-albertovich]

In modify.c these setup exit paths seem to require this call teardown(ctx); :

1. Line 313
2. Line 332

Other than that and the comment I made in the code it looks good, thank you for taking the time to address this issue.

[nokute78]

I added missing teardown and remove unused variables from test code.