🐛 Reset workDirDepth in cdroot() (#22441)

Marlin/src/sd/cardreader.cpp

@@ -1024,6 +1024,7 @@ int8_t CardReader::cdup() {
 void CardReader::cdroot() {
   workDir = root;
   flag.workDirIsRoot = true;
+  workDirDepth = 0;
   TERN_(SDCARD_SORT_ALPHA, presort());
 }