Prevent wdt reset during file listing

Firmware/Marlin_main.cpp

@@ -5681,6 +5681,7 @@ if(eSoundMode!=e_SOUND_MODE_SILENT)
     - `L` - Reports ling filenames instead of just short filenames. Requires host software parsing.
     */
     case 20:
+      KEEPALIVE_STATE(NOT_BUSY); // do not send busy messages during listing. Inhibits the output of manage_heater()
       SERIAL_PROTOCOLLNRPGM(_N("Begin file list"));////MSG_BEGIN_FILE_LIST
       card.ls(code_seen('L'));
       SERIAL_PROTOCOLLNRPGM(_N("End file list"));////MSG_END_FILE_LIST

Firmware/cardreader.cpp

@@ -133,6 +133,7 @@ void CardReader::lsDive(const char *prepend, SdFile parent, const char * const m
 							printf_P(PSTR("\"%s\" "), LONGEST_FILENAME);
 						
 						SERIAL_PROTOCOLLN(p.fileSize);
+						manage_heater();
 						break;
 				
 					case LS_GetFilename: