Guard Trader result dropdown tooltip against stale state (#9742)

* fix(trade): guard nil sortedResultTbl in dropdown tooltipFunc

The nil guard lost during the vaisest/trader-improvements merge
caused a crash when hovering the result dropdown after clearing
search results.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test(trade): cover stale result dropdown tooltip guards

* style(spec): use tab indentation in TradeQuery test

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: mcagnion

spec/System/TestTradeQuery_spec.lua

@@ -0,0 +1,57 @@
+describe("TradeQuery", function()
+	describe("result dropdown tooltipFunc", function()
+		-- Builds a TradeQuery with the strict minimum needed for
+		-- PriceItemRowDisplay to construct row 1 without exploding. Only the
+		-- two itemsTab subtables read by the slot lookup at the top of
+		-- PriceItemRowDisplay need to be created here; everything else either
+		-- lives behind a callback we never trigger, or is already initialized
+		-- by the TradeQuery constructor.
+		local function newTradeQuery(state)
+			local tq = new("TradeQuery", { itemsTab = {} })
+			tq.itemsTab.activeItemSet = {}
+			tq.itemsTab.slots         = {}
+			tq.slotTables[1] = { slotName = "Ring 1" }
+			if state.resultTbl       then tq.resultTbl       = state.resultTbl       end
+			if state.sortedResultTbl then tq.sortedResultTbl = state.sortedResultTbl end
+			return tq
+		end
+
+		-- Builds row 1 of the trader UI and returns the dropdown that owns the
+		-- tooltipFunc we want to exercise.
+		local function buildRow1Dropdown(tq)
+			tq:PriceItemRowDisplay(1, nil, 0, 20)
+			return tq.controls.resultDropdown1
+		end
+
+		it("returns early when sortedResultTbl[row_idx] is missing", function()
+			-- No sorted results at all -> first guard must short-circuit.
+			local tq = newTradeQuery({})
+			local dropdown = buildRow1Dropdown(tq)
+			local tooltip = new("Tooltip")
+
+			assert.has_no.errors(function()
+				dropdown.tooltipFunc(tooltip, "DROP", 1, nil)
+			end)
+			assert.are.equal(0, #tooltip.lines)
+		end)
+
+		it("returns early when the backing result entry has been cleared", function()
+			-- The dropdown must be built against a valid result so that
+			-- PriceItemRowDisplay's construction loop succeeds; we wipe
+			-- resultTbl[1] only afterwards, to simulate a stale tooltip
+			-- callback firing after the results were invalidated.
+			local tq = newTradeQuery({
+				resultTbl       = { [1] = { [1] = { item_string = "Rarity: RARE\nBehemoth Hold\nGold Ring" } } },
+				sortedResultTbl = { [1] = { { index = 1 } } },
+			})
+			local dropdown = buildRow1Dropdown(tq)
+			tq.resultTbl[1] = {}
+			local tooltip = new("Tooltip")
+
+			assert.has_no.errors(function()
+				dropdown.tooltipFunc(tooltip, "DROP", 1, nil)
+			end)
+			assert.are.equal(0, #tooltip.lines)
+		end)
+	end)
+end)

src/Classes/TradeQuery.lua

@@ -1093,8 +1093,15 @@ function TradeQueryClass:PriceItemRowDisplay(row_idx, top_pane_alignment_ref, ro
 		end
 	end
 	controls["resultDropdown"..row_idx].tooltipFunc = function(tooltip, dropdown_mode, dropdown_index, dropdown_display_string)
-		local pb_index = self.sortedResultTbl[row_idx][dropdown_index].index
-		local result = self.resultTbl[row_idx][pb_index]
+		local sortedRow = self.sortedResultTbl[row_idx]
+		if not sortedRow or not sortedRow[dropdown_index] then
+			return
+		end
+		local pb_index = sortedRow[dropdown_index].index
+		local result = self.resultTbl[row_idx] and self.resultTbl[row_idx][pb_index]
+		if not result then
+			return
+		end
 		local item = new("Item", result.item_string)
 		tooltip:Clear()
 		if slotTbl.slotName == "Watcher's Eye" then