MINOR: applet: always use task_new_on() on applet creation

Now that task_new_on() supports negative numbers, there's no need for
checking the thread value nor falling back to task_new_anywhere().
diff --git a/src/applet.c b/src/applet.c
index 47263bc..41ad2fc 100644
--- a/src/applet.c
+++ b/src/applet.c
@@ -57,11 +57,7 @@
 	}
 	appctx->sedesc = sedesc;
 
-	if (thr >= 0)
-		appctx->t = task_new_on(thr);
-	else
-		appctx->t = task_new_anywhere();
-
+	appctx->t = task_new_on(thr);
 	if (unlikely(!appctx->t))
 		goto fail_task;
 	appctx->t->process = task_run_applet;