Fix Flowframes hang detection (watchdog never fired on frozen log)

[NetsumaInfo]

Problem

Flowframes can stop responding mid-interpolation after some time: the process
stays alive but its session log stops growing. A 60s progress watchdog already
existed to catch this, but it never fired, so the job hung indefinitely until
manually paused.

Root cause

lastLogTime was refreshed on every poll tick whenever the session log file
merely read successfully, not only when new lines were written. A
frozen-but-readable log therefore kept resetting the timer, so
Date.now() - lastLogTime > 60000 was never true.

Fix

• Only bump lastLogTime when new log lines actually appear
  (lines.length > lastLineCount).
• Add a grace check so a quiet encode phase is not false-killed: if the newest
  output file is still growing, reset the timer instead of failing.

On a genuine hang the job now errors out after 60s and the queue moves on,
instead of hanging forever.

Scope

One file, AniSmooth/js/utils/flowframesHandler.js (+16/-1). No other changes.

Testing

• node --check passes.
• JS runs live in dev (no rebuild); reload the extension in AE.