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/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);