Reimplement #2892

Include #2892 to fix the isHeating symbol in the extruder graphics

Marlin/dogm_lcd_implementation.h

   lcd_print(itostr3(int(heater >= 0 ? degHotend(heater) : degBed()) + 0.5));
 
   lcd_printPGM(PSTR(LCD_STR_DEGREE " "));
-  if (!isHeatingHotend(0)) {
+  if (heater >= 0 ? !isHeatingHotend(heater) : !isHeatingBed()) {
     u8g.drawBox(x+7,y,2,2);
   }
   else {