Core/Unit: Creature that are in combat but not engaged or with offline reference threat don't execute the reset

[Killyana]

Description: When a creature is in combat but not engaged or with an offline reference threat, the reset hook will not be executed.

Steps to reproduce the problem:

1. use this sql DB/Quest: The Ata'mal Terrace #21570 (comment)
2. .go c id 22061
3. hit the npc and wait until Shadowlord Deathwail cast a fire ball
4. .deb threat on Shadowlord Deathwail to check the threat list, and npc inf to see he's in combat
5. .GM ON and notice the reset script is not executed (it must set unit flags immune to pc and npc)

Second case:

1. revert 1bdc792
2. .go game 150441
3. pull the lever
4. the boss will be set in combat with you char (get combat and threat state)
5. .gm on
6. notice reset is not executed : 1bdc792#diff-361226ee2d7dc2bfd9b9d27273a3bad2L58

Third case: (the easiest one to reproduce)

1. Connect a horde char (gm on)
2. .npc add temp 321
3. move 20-30 yard to avoid aggro
4. select the npc and .cast back 38312
5. notice you're in combat
6. .npc inf (* UNIT_FLAG_IN_COMBAT (0x80000))
7. .deb threat:
   Brother Deros (GUID 1) does not threaten any units.
   Brother Deros (GUID 1, SpawnID 0) is not currently engaged.
8. .aura 1243 the npc
9. .Gm ON (notice the aura is still there, it means no reset() was executed)

Branch(es): 3.3.5

TC rev. hash/commit: rev. 596b2d1

[Killyana]

Same issue here: https://github.com/TrinityCore/TrinityCore/blob/3.3.5/src/server/scripts/Kalimdor/BlackfathomDeeps/blackfathom_deeps.cpp#L129

1. .go game 32930
2. Kill the npc that aggro then activate one of the [Fire of Aku'mai]
3. you we be set in combat with the summoned npcs but they will not aggro

Aku'mai Snapjaw (GUID 230, SpawnID 0) is not engaged, but still has a threat list? Well, here it is:
   1.   Tert   (GUID 15)  - threat 0.000000
End of threat list.

[Jildor]

I think same happens with Fire Cyclone triggers on Sartharion
https://tcubuntu.northeurope.cloudapp.azure.com/aowow/?npc=30648

[jackpoz]

Same issue here: https://github.com/TrinityCore/TrinityCore/blob/3.3.5/src/server/scripts/Kalimdor/BlackfathomDeeps/blackfathom_deeps.cpp#L129

1. .go game 32930
2. Kill the npc that aggro then activate one of the [Fire of Aku'mai]
3. you we be set in combat with the summoned npcs but they will not aggro

Aku'mai Snapjaw (GUID 230, SpawnID 0) is not engaged, but still has a threat list? Well, here it is:
   1.   Tert   (GUID 15)  - threat 0.000000
End of threat list.

This case works fine for me:
https://imgur.com/j5r6PV7

[jackpoz]

Try 3.3.5...jackpoz:fixes/3.3.5-combat-but-not-engaged for the 1st and 3rd case (the ones I tried).
Please note the 1st case is escorting and that doesn't seem to call Reset() when it reaches the point where it's supposed to go. It does enters evade mode though.