UScreen 1.2.4 — USB second monitor for Linux with S Pen support

For the one tablet that shows a single frame, and two small things in the settings window.

Decoder: a ladder instead of a loop

A Galaxy Tab S10 FE+ on Android 16 decodes keyframes and produces nothing for
the frames in between, so 1.2.3's watchdog restarted the decoder every 1.5 s,
got one frame at the next keyframe, and called that recovered — the picture
blinked at 1 fps (#10).

Now two stalls move the app one step down: the hardware decoder, then the
hardware decoder without low-latency hints, then Android's software decoder,
which is slow at tablet resolutions but decodes anything. Thirty frames in a
row count as recovery; one does not. The decoder's name and output format are
logged, so a logcat names the component.

Frames are also stamped 10 ms apart now instead of 1 µs — the host's sequence
number still rides in the timestamp for the latency loop, but a decoder that
paces or drops frames by timestamp finally sees plausible ones. This may be
the whole cause on that tablet; it is verified only in the sense that every
number still divides out. Reports from other devices welcome either way.

Settings window

• It scrolls. The settings ran past the window with no scrollbar and a dead
  wheel, so on a small or portrait screen the lower ones were unreachable
  (#14).
• Saving from it no longer erases the address remembered by uscreen wifi
  — the window rewrites the whole config file and did not know that field.

Update both halves together. Files: .deb, .rpm, PKGBUILD archive,
portable tarball, uscreen.apk, SHA256SUMS.