better handling of BTN_USER_PRESSED definition

examples/companion_radio/UITask.cpp

@@ -4,6 +4,10 @@
 
 #define AUTO_OFF_MILLIS   15000   // 15 seconds
 
+#ifndef USER_BTN_PRESSED
+#define USER_BTN_PRESSED LOW
+#endif
+
 // 'meshcore', 128x13px
 static const uint8_t meshcore_logo [] PROGMEM = {
     0x3c, 0x01, 0xe3, 0xff, 0xc7, 0xff, 0x8f, 0x03, 0x87, 0xfe, 0x1f, 0xfe, 0x1f, 0xfe, 0x1f, 0xfe,