fix: client timer fallback re-sent CMSG_GAMEOBJ_USE and cleared loot guid

When the client-side cast timer expired slightly before SMSG_SPELL_GO
arrived, the fallback at update():1367 called performGameObjectInteraction
Now which sent a DUPLICATE CMSG_GAMEOBJ_USE to the server (confusing its
GO state machine), then resetCastState() cleared lastInteractedGoGuid_.
When SMSG_SPELL_GO finally arrived, the guid was gone so CMSG_LOOT was
never sent — quest chests produced no loot window.

Fix: the fallback no longer re-sends USE (server drives the interaction
via SMSG_SPELL_GO). resetCastState() no longer clears
lastInteractedGoGuid_ so the SMSG_SPELL_GO handler can still send LOOT.

src/game/spell_handler.cpp

@@ -1619,7 +1619,11 @@ void SpellHandler::resetCastState() {
     queuedSpellId_ = 0;
     queuedSpellTarget_ = 0;
     owner_.pendingGameObjectInteractGuid_ = 0;
-    owner_.lastInteractedGoGuid_ = 0;
+    // lastInteractedGoGuid_ is intentionally NOT cleared here — it must survive
+    // until handleSpellGo sends CMSG_LOOT after the server-side cast completes.
+    // handleSpellGo clears it after use (line 958). Previously this was cleared
+    // here, which meant the client-side timer fallback destroyed the guid before
+    // SMSG_SPELL_GO arrived, preventing loot from opening on quest chests.
 }
 
 void SpellHandler::resetAllState() {