fix(scrolls): don't cache scrolls whose tooltip scraped empty

TryResolve cached an entry even when ScanItemTooltip returned 0 lines
(empty string is truthy in Lua), so empty-tooltip scrolls were treated
as cache hits forever and never retried - and per-pass stats disagreed
with the cache. Only cache once at least one tooltip line was captured,
and treat cached-but-empty entries (stale SavedVariables) as misses.

CoaExporter/Collectors/MysticScrolls.lua

@@ -71,7 +71,8 @@ end
 
 local function TryResolve(entry)
     local cache = CoaExporterScrollCache.entries
-    if cache[entry.itemID] and cache[entry.itemID].itemTooltip then
+    local hit = cache[entry.itemID]
+    if hit and hit.itemTooltip and hit.itemTooltip ~= "" then
         return true
     end
     local name, _, quality = GetItemInfo(entry.itemID)
@@ -82,6 +83,11 @@ local function TryResolve(entry)
         return false
     end
     local itemLines = ScanItemTooltip(entry.itemID)
+    if #itemLines == 0 then
+        -- Tooltip not server-resolved yet; don't cache an empty entry, or
+        -- this scroll would never be retried on later passes.
+        return false
+    end
     local spellName, spellRank
     if GetItemSpell then
         spellName, spellRank = GetItemSpell(entry.itemID)
@@ -97,7 +103,7 @@ local function TryResolve(entry)
         itemTooltip = table.concat(itemLines, "\n"),
         fetchedAt = time(),
     }
-    return #itemLines > 0
+    return true
 end
 
 function AE.ScrollsScanPass()