ft-floatd: a launch for a missing app no longer kills the control socket

Gio.DesktopAppInfo.new() returns NULL for a desktop file that doesn't
exist, and PyGObject raises TypeError ("constructor returned NULL")
rather than returning None, so launch()'s `if info is None` never ran.
The exception escaped the control socket's GLib callback, GLib dropped
the watch, and ft-floatd stopped answering everything: the float key,
dock, Launch as Standalone, and profiles, until the desktop restarted.

Found on the Frame (2026-10-02): a profile saved with RustDesk's
Flatpak open records its window's app id, com.carriez.flutter_hbb,
which has no desktop file (the Flatpak's is com.rustdesk.RustDesk).
`ft-layout use` on that profile asked ft-floatd to launch it, and
ft-floatd went silent. With this, that launch replies "error no app
com.carriez.flutter_hbb" and the profile's other apps open.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -17,6 +17,8 @@ Join the [Frametop Discord](https://discord.gg/W3X9f7z3Bc) for questions, ideas,
 
 ## Install on the headset
 
+> **Frametop doesn't work on the SteamOS beta right now.** On the beta (SteamOS 0.4.3), gaze mode can't read the eye tracker, and the desktop has started without its taskbar ([#15](https://github.com/DeeJanuz/frametop/issues/15)). Use the stable SteamOS release until this note is gone.
+
 You need a Steam Frame with an internet connection, a keyboard (Bluetooth, or the on-screen one), and about 3 GB of free space.
 
 1. In the launcher, choose Launch a program → Desktop.

float/ft_floatd.py

@@ -745,7 +745,10 @@ class Daemon:
         Returns (reply, pid or None)."""
         if app:
             app = app.removesuffix(".desktop")
+            try:
                 info = Gio.DesktopAppInfo.new(app + ".desktop")
+            except TypeError:  # PyGObject raises for the NULL a missing desktop file returns
+                info = None
             if info is None:
                 return f"error no app {app}", None
             pids = []