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")];

wled00/util.cpp

@@ -336,7 +336,7 @@ uint8_t extractModeSlider(uint8_t mode, uint8_t slider, char *dest, uint8_t maxL
           case 0:  strncpy_P(dest, PSTR("FX Speed"), maxLen); break;
           case 1:  strncpy_P(dest, PSTR("FX Intensity"), maxLen); break;
         }
-        dest[maxLen] = '\0'; // strncpy does not necessarily null terminate string
+        dest[maxLen-1] = '\0'; // strncpy does not necessarily null terminate string
       }
     }
     return strlen(dest);