fix(launcher): dead rows no longer starve FIND MODS thumbnails

_queueFindEnrichment allows two thumbnail starts per frame, but it counted a
row against that allowance even when _startFindThumb ignored it. A row already
resolved to "failed", or with no thumbnail at all, is ignored there, so two such
rows above a card spent the allowance every frame and the card never got a
download. It stayed on its MOD placeholder (no spinner) for the whole session.

Skip rows that have already resolved, so only a row that actually starts a
download is counted. Adds a regression test that fails without the change.

src/import/RomImporter.lua

@@ -8503,8 +8503,12 @@ function RomImporter:_queueFindEnrichment()
   if not visible then return end
   local thumbnails, stats = 0, 0
   for _, entry in ipairs(visible) do
+    -- A row already resolved to "failed" (or with no thumbnail at all) must not
+    -- spend this frame's allowance: _startFindThumb ignores it, so counting it
+    -- let two dead rows above a card starve it of a download forever.
     if thumbnails < FIND_ENRICH_PER_FRAME
         and self:_findThumb(entry) == nil
+        and not (self._findThumbs and self._findThumbs[entry.id] ~= nil)
         and not self:_findThumbPending(entry.id) then
       self:_startFindThumb(entry)
       thumbnails = thumbnails + 1

tests/engine/launcher_navigation_perf.lua

@@ -65,6 +65,27 @@ do
     "update schedules a bounded thumbnail and stats batch for visible rows")
 end
 
+-- Rows already resolved to "failed" (or with no thumbnail) must not spend the
+-- per-frame download allowance, or two of them above a card starve it forever.
+do
+  local started = {}
+  local imp = setmetatable({ tab = "find", findLoaded = true,
+    _findThumbs = { dead1 = false, dead2 = false },
+    _findVisibleEntries = {
+      { id = "dead1", thumbnail = "https://example.invalid/1.png" },
+      { id = "dead2", thumbnail = "https://example.invalid/2.png" },
+      { id = "dead3" },
+      { id = "alive", thumbnail = "https://example.invalid/alive.png" },
+    } }, RomImporter)
+  imp._findThumbPending = function() return false end
+  imp._findStatsCached = function() return {} end
+  imp._startFindThumb = function(_, entry) started[#started + 1] = entry.id end
+  imp:_queueFindEnrichment()
+  eq(#started, 1, "only the row that can load starts a download")
+  eq(started[1], "alive",
+    "dead rows above a card do not starve it of its download")
+end
+
 do
   local requests = 0
   local imp = setmetatable({}, RomImporter)