[Fishing] Fishing skill bonuses from items not correctly calculated

[Meanb0b]

WoW Freakz item link: https://www.wow-freakz.com/item_finder.php?item=88710&&name=nat-s-hat
https://www.wow-freakz.com/item_finder.php?item=133755&&name=underlight-angler
https://www.wow-freakz.com/item_finder.php?item=153203&&name=ancient-fishing-line
https://www.wow-freakz.com/item_finder.php?item=19969&&name=nat-pagle-s-extreme-anglin-boots
Bug description: The effective fishing skill (including bonuses from several items) is not calculated correctly. Having multiple of them equiped at the same time seems to confuse the skill calculator. I made some screenshots to demonstrate the issue.
(Unfortunately, imgur mixed up my screenshot order, sorry about that)
1st: base skill 804 - correct
2nd: equipping Underlight Angler (+60) with Ancient Fishing Line (+6) results in +66 - correct
3rd: Equipping Nat's Hat (+5) + Underlight Angler (+66) results in +71 - correct
4th: Equipping Nat Pagle's Extreme Anglin' Boots (+5) + Underlight Angler (+66) WITHOUT Nat's Hat results in +71 - correct
5th: Equipping Nat Pagle's Extreme Anglin' Boots (+5) + Underlight Angler (+66) + Nat's Hat (+5) still results in +71 instead of +76 - wrong!
Same result when I equip hat before boots or the other way round - doesn't work.
I even tried it using just hat + boots without the Underlight Angler to see if it caps at 875 - but still only counts +5 skill.
Proof: https://imgur.com/a/K4goruL

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