trying to reduce flickering

The NeoPixelBus RMT driver seems to get stalled when ESP.get.... functions are called (big kernel lock?). Also its glitching during flash file access.

This change tries to avoid some conflicts by first checking that the driver is not sending.

wled00/file.cpp

@@ -35,6 +35,14 @@ static File f; // don't export to other cpp files
 
 //wrapper to find out how long closing takes
 void closeFile() {
+  #ifdef ARDUINO_ARCH_ESP32
+  // WLEDMM: file.close() triggers flash writing. While flash is writing, the NPB RMT driver cannot fill its buffer which may create glitches.
+  unsigned long t_wait = millis();
+  while(strip.isUpdating() && (millis() - t_wait < 72)) delay(1); // WLEDMM try to catch a moment when strip is idle
+  while(strip.isUpdating() && (millis() - t_wait < 96)) delay(0); //        try harder
+  //if (strip.isUpdating()) USER_PRINTLN("closeFile: strip still updating.");
+  delay(2); // might help
+  #endif
   #ifdef WLED_DEBUG_FS
     DEBUGFS_PRINT(F("Close -> "));
     uint32_t s = millis();