minor bugfixes as suggested by the rabbit

- PulLightControl UM: dont release a lock you do not own
- off-by-one error in extractModeSlider (used only in rotary in UM)
- safety check in playlist in case something goes horribly wrong

wled00/playlist.cpp

@@ -89,7 +89,8 @@ int16_t loadPlaylist(JsonObject playlistObj, byte presetId) {
       it++;
     }
   }
-  for (int i = it; i < playlistLen; i++) playlistEntries[i].dur = playlistEntries[it -1].dur;
+  if (it > 0) // should never happen but just in case
+    for (int i = it; i < playlistLen; i++) playlistEntries[i].dur = playlistEntries[it -1].dur;
 
   it = 0;
   JsonArray tr = playlistObj[F("transition")];