avoid glitches at relay power-on

* switch on relay _after_ the current leds transmission is complete.

wled00/button.cpp

@@ -389,6 +389,7 @@ void handleIO()
       esp32RMTInvertIdle();
       #endif
       if (rlyPin>=0) {
+        if (strip.isUpdating()) delay(FRAMETIME_FIXED); // WLEDMM avoids randomly colored pixles at power-on
         pinMode(rlyPin, OUTPUT);
         digitalWrite(rlyPin, !rlyMde);
       }

wled00/wled.cpp

@@ -893,10 +893,10 @@ void WLED::setup()
 void WLED::beginStrip()
 {
   // Initialize NeoPixel Strip and button
+  strip.fill(BLACK);    // WLEDMM avoids random colors at power-on
   strip.finalizeInit(); // busses created during deserializeConfig()
   strip.makeAutoSegments();
-  strip.setBrightness(0);
-  strip.fill(BLACK);    // WLEDMM avoids random colors at power-on
+  strip.setBrightness(0, true); // WLEDMM directly apply BLACK (no transition time)
   strip.setShowCallback(handleOverlayDraw);
 
   if (turnOnAtBoot) {
@@ -915,9 +915,11 @@ void WLED::beginStrip()
 
   // init relay pin
   if (rlyPin>=0) {
-    delay(FRAMETIME_FIXED); // WLEDMM wait a bit, to ensure that no background led communication is happening while powering on the strip
+    if (strip.isUpdating()) delay(FRAMETIME_FIXED); // WLEDMM ensure that no background led communication is happening while powering on the strip
     digitalWrite(rlyPin, (rlyMde ? bri : !bri));
-    delay(50); // wait for relay to switch and power to stabilize
+    delay(75); // wait for relay to switch and power to stabilize
+    strip.show(); // update LEDs
+    delay(5);
   }
 }