buffs: cancel by spellID instead of GetPlayerBuff slot index

`GetPlayerBuff(PLAYER_BUFF_START_ID + this.id, filter)` assumes the
visual index pfUI shows matches the engine's slot order. When that
mismapping happens — most easily reproduced by stacking buffs that
share a slot family — right-clicking one buff cancels another.

`C_Spell.CancelSpellByID(spellID)` ships CMSG_CANCEL_AURA keyed to the
spell, not a slot, so it's immune to whatever order the slot table is
in. Cache `spellId` on the button at refresh time in buff.lua; in the
unitframes/buffwatch handlers fetch the aura fresh via
`C_UnitAuras.GetAuraDataByIndex` at click time.

Fixes #10.

api/unitframes.lua

@@ -73,8 +73,8 @@ end
 
 local function BuffOnClick()
   if this:GetParent().label == "player" then
-    local bid = GetPlayerBuff(PLAYER_BUFF_START_ID + this.id, "HELPFUL")
-    if bid >= 0 then CancelPlayerBuff(bid) end
+    local aura = C_UnitAuras.GetAuraDataByIndex("player", this.id, "HELPFUL")
+    if aura and aura.spellId then C_Spell.CancelSpellByID(aura.spellId) end
   end
 end
 
@@ -114,8 +114,8 @@ end
 
 local function DebuffOnClick()
   if this:GetParent().label == "player" then
-    local bid = GetPlayerBuff(PLAYER_BUFF_START_ID + this.id, "HARMFUL")
-    if bid >= 0 then CancelPlayerBuff(bid) end
+    local aura = C_UnitAuras.GetAuraDataByIndex("player", this.id, "HARMFUL")
+    if aura and aura.spellId then C_Spell.CancelSpellByID(aura.spellId) end
   end
 end
 

modules/buff.lua

@@ -60,6 +60,7 @@ pfUI:RegisterModule("buff", function ()
       buff.mode = buff.btype
       buff.expirationTime = aura.expirationTime
       buff.stackCount = aura.applications
+      buff.spellId = aura.spellId
       buff.texture:SetTexture(aura.icon)
 
       if buff.btype == "HARMFUL" then
@@ -146,9 +147,8 @@ pfUI:RegisterModule("buff", function ()
         CancelItemTempEnchantment(1)
       elseif CancelItemTempEnchantment and this.mode and this.mode == "OFFHAND" then
         CancelItemTempEnchantment(2)
-      else
-        local bid = GetPlayerBuff(PLAYER_BUFF_START_ID + this.id, this.btype)
-        if bid >= 0 then CancelPlayerBuff(bid) end
+      elseif this.spellId then
+        C_Spell.CancelSpellByID(this.spellId)
       end
     end)
 

modules/buffwatch.lua

@@ -99,8 +99,8 @@ pfUI:RegisterModule("buffwatch", function ()
         DEFAULT_CHAT_FRAME:AddMessage("|cff33ffcc" .. skill .. "|r" .. T["is now blacklisted."])
       end
     elseif this.parent.unit == "player" then
-      local bid = GetPlayerBuff(PLAYER_BUFF_START_ID + this.id, this.type)
-      if bid >= 0 then CancelPlayerBuff(bid) end
+      local aura = C_UnitAuras.GetAuraDataByIndex("player", this.id, this.type)
+      if aura and aura.spellId then C_Spell.CancelSpellByID(aura.spellId) end
     end
   end
 

skins/blizzard/character.lua

@@ -136,22 +136,19 @@ pfUI:RegisterSkin("Character", function ()
       end
     end
 
-    HookScript(CharacterFrame, "OnShow", function()
+    hooksecurefunc("CharacterFrame_OnShow", function()
       RefreshCharacterSlots()
       RefreshPetPosition()
+    end)
 
-      if not this.hooked then
-        hooksecurefunc("PaperDollItemSlotButton_Update", function()
-          -- update only character slots!
-          if string.find(this:GetName(), "^Character.-Slot$") then
-            RefreshCharacterSlot(this)
-          end
-        end)
-        hooksecurefunc("PetTab_Update", RefreshPetPosition)
-        this.hooked = true
+    hooksecurefunc("PaperDollItemSlotButton_Update", function()
+      if this:GetParent() == PaperDollFrame then
+        RefreshCharacterSlot(this)
       end
     end)
 
+    hooksecurefunc("PetTab_Update", RefreshPetPosition)
+
     StripTextures(PaperDollFrame)
     StripTextures(CharacterAttributesFrame)
     StripTextures(CharacterResistanceFrame)