fix: a new playback raced the previous one for the audio device

Reported precisely: press play again and it stops the current message, but you
then have to wait the whole length of the message before it will play — otherwise
the radio is keyed and the PTT released at once.

Play only SIGNALLED the previous playback to stop and started a new one straight
away. The old goroutine still held the WASAPI render client for a moment, so the
new client could not start; it returned immediately and the PTT tail was all that
was left. The log now shows both halves of that: a play line, then a release
120 ms later.

Stopping now waits for the goroutine to have returned — the point of stopping
before starting again — bounded at 1.5 s so a wedged device cannot freeze the
operator's click, and saying so in the log if it ever comes to that.

changelog.json

@@ -4,11 +4,13 @@
     "date": "",
     "en": [
       "Cluster filters gain NEW POTA and NEW COUNTY, alongside the existing status chips.",
-      "A playback that fails to start now says so in the log instead of ending silently after a tenth of a second."
+      "A playback that fails to start now says so in the log instead of ending silently after a tenth of a second.",
+      "Replaying a recording before the previous one has finished now works: the new playback waits for the audio device to be free instead of keying the radio and releasing at once."
     ],
     "fr": [
       "Les filtres du cluster gagnent NEW POTA et NEW COUNTY, à côté des pastilles de statut existantes.",
-      "Une lecture qui ne démarre pas le signale désormais dans le journal, au lieu de s'arrêter en silence au bout d'un dixième de seconde."
+      "Une lecture qui ne démarre pas le signale désormais dans le journal, au lieu de s'arrêter en silence au bout d'un dixième de seconde.",
+      "Relancer un enregistrement avant la fin du précédent fonctionne désormais : la nouvelle lecture attend que le périphérique audio soit libre, au lieu de passer en émission et de relâcher aussitôt."
     ]
   },
   {