potentiometer: check that pin supports ananlogread

newer esp32 frameworks will throw lots of warnings when trying to read from a non-analog pin.

wled00/button.cpp

@@ -156,6 +156,7 @@ void handleAnalog(uint8_t b)
   #ifdef ESP8266
   rawReading = analogRead(A0) << 2;   // convert 10bit read to 12bit
   #else
+  if ((btnPin[b] < 0) || (digitalPinToAnalogChannel(btnPin[b]) < 0)) return; // pin must support analog ADC - newer esp32 frameworks throw lots of warnings otherwise
   rawReading = analogRead(btnPin[b]); // collect at full 12bit resolution
   #endif
   yield();                            // keep WiFi task running - analog read may take several millis on ESP8266
@@ -188,7 +189,7 @@ void handleAnalog(uint8_t b)
       if (aRead == 0) {
         briLast = bri;
         bri = 0;
-      } else{
+      } else {
         bri = aRead;
       }
     } else if (macroDoublePress[b] == 249) {