Second attempt at fixing transaction use-after-free

The solution used in 073ac425d5 doesn't
work in all cases because the freed instruction might be ahead in the
list, not necessarily behind.

The new solution delays running the queue until after the loop has
finished iterating, thus avoiding the problem completely.

sway/desktop/transaction.c

@@ -344,13 +344,11 @@ static void set_instruction_ready(
 
 	}
 
-	// If all views are ready, apply the transaction.
 	// If the transaction has timed out then its num_waiting will be 0 already.
 	if (transaction->num_waiting > 0 && --transaction->num_waiting == 0) {
 		if (!txn_debug) {
 			wlr_log(WLR_DEBUG, "Transaction %p is ready", transaction);
 			wl_event_source_timer_update(transaction->timer, 0);
-			transaction_progress_queue();
 		}
 	}
 }
@@ -364,15 +362,10 @@ static void set_instructions_ready(struct sway_view *view, int index) {
 		struct sway_transaction_instruction *instruction =
 			view->swayc->instructions->items[i];
 		if (!instruction->ready) {
-			// set_instruction_ready can remove instructions from the list we're
-			// iterating
-			size_t length = view->swayc->instructions->length;
 			set_instruction_ready(instruction);
-			size_t num_removed = length - view->swayc->instructions->length;
-			i -= num_removed;
-			index -= num_removed;
 		}
 	}
+	transaction_progress_queue();
 }
 
 void transaction_notify_view_ready(struct sway_view *view, uint32_t serial) {