automod: recover from panics in applying effects

[jo3-l]

This PR is one of several aiming to mitigate the impact of bugs similar to those introduced in the previous release.

The most pressing issue was the inadvertent removal of a nil guard in KickUser by me in #1659, which caused panics which were difficult to track down. To make these easier to debug in future (and to prevent complete bot crashes), in this PR we recover and log a stacktrace for panics in applying advanced automod effects and basic automod punishments. This supercedes the temporary bandaid recover added directly to KickUser in f9602a1.

For reference, I compiled a version of the bot with the nil pointer bug re-added (but with this patch applied as well.) Instead of crashing, the following is logged instead:

ERRO recovered from panic applying automod effect
runtime error: invalid memory address or nil pointer dereference
goroutine 379 [running]:
runtime/debug.Stack()
        /usr/local/go/src/runtime/debug/stack.go:24 +0x5e
github.com/botlabs-gg/yagpdb/v2/automod.(*Plugin).RulesetRulesTriggeredCondsPassed.func1.1()
        /REDACTED/yagpdb/automod/automod_bot.go:477 +0x38
panic({0x14a1cc0?, 0x492e600?})
        /usr/local/go/src/runtime/panic.go:770 +0x132
github.com/botlabs-gg/yagpdb/v2/moderation.KickUser(0x7ffa19f13270?, 0xad7ea432382000a, 0x0, 0x0, 0xc0000f8480, {0xc001908de0, 0x18}, 0xc00065ea00, 0xffffffffffffffff)
         /REDACTED/yagpdb/moderation/punishments.go:236 +0xf1
github.com/botlabs-gg/yagpdb/v2/automod.(*KickUserEffect).Apply(0x4931210?, 0xc0003f7860, {0x13b8c20?, 0xc000399dd0?})
         /REDACTED/yagpdb/automod/effects.go:272 +0xb2
github.com/botlabs-gg/yagpdb/v2/automod.(*Plugin).RulesetRulesTriggeredCondsPassed.func1(0xc00053bf00, 0xc0003f7860?)
         /REDACTED/yagpdb/automod/automod_bot.go:482 +0xf2
created by github.com/botlabs-gg/yagpdb/v2/automod.(*Plugin).RulesetRulesTriggeredCondsPassed in goroutine 473
        /REDACTED/yagpdb/automod/automod_bot.go:474 +0xd68  p=automod_v2 stck="automod.(*Plugin).RulesetRulesTriggeredCondsPassed.func1.1:automod_bot.go:478"

which points directly to the problematic line.

[jo3-l]

This recover is completely safe to remove given the other patches in this PR. KickUser is called from three locations in the source:

• once in the kick command (commands.go:313)
  • We already recover from panics in command executions.
• once in automod legacy (automod_legacy/bot.go:167)
  • The necessary panic handler is added in this PR.
• and once in advanced automod via the kick user effect (automod/effects.go:272).
  • The necessary panic handler is added in this PR.

hence, there is no need for a separate recover directly in KickUser anymore.