Preserve CWD for write/remove file (#16667)

Marlin/src/sd/cardreader.cpp

   stopSDPrint();
 
   SdFile *curDir;
-  const char * const fname = diveToFile(curDir, path);
+  const char * const fname = diveToFile(true, curDir, path);
   if (!fname) return;
 
   if (file.open(curDir, fname, O_READ)) {
   stopSDPrint();
 
   SdFile *curDir;
-  const char * const fname = diveToFile(curDir, path);
+  const char * const fname = diveToFile(false, curDir, path);
   if (!fname) return;
 
   if (file.open(curDir, fname, O_CREAT | O_APPEND | O_WRITE | O_TRUNC)) {
   //stopSDPrint();
 
   SdFile *curDir;
-  const char * const fname = diveToFile(curDir, name);
+  const char * const fname = diveToFile(false, curDir, name);
   if (!fname) return;
 
   if (file.remove(curDir, fname)) {
  *
  * A nullptr result indicates an unrecoverable error.
  */
-const char* CardReader::diveToFile(SdFile*& curDir, const char * const path, const bool echo/*=false*/) {
+const char* CardReader::diveToFile(const bool update_cwd, SdFile*& curDir, const char * const path, const bool echo/*=false*/) {
   // Track both parent and subfolder
   static SdFile newDir1, newDir2;
   SdFile *sub = &newDir1, *startDir;
 
+  // Parsing the path string
   const char *item_name_adr = path;
-  if (path[0] == '/') {
+
+  if (path[0] == '/') {               // Starting at the root directory?
     curDir = &root;
-    workDirDepth = 0;
+    if (update_cwd) workDirDepth = 0; // The cwd can be updated for the benefit of sub-programs
     item_name_adr++;
   }
   else
-    curDir = &workDir;
+    curDir = &workDir;                // Dive from workDir (as set by the UI)
 
   startDir = curDir;
-
-  // Start dive
   while (item_name_adr) {
-    // Find next sub
+    // Find next subdirectory delimiter
     char * const name_end = strchr(item_name_adr, '/');
+
+    // Last atom in the path? Item found.
     if (name_end <= item_name_adr) break;
 
     // Set subDirName
     // curDir now subDir
     curDir = sub;
 
-    // Update workDirParents and workDirDepth
-    if (workDirDepth < MAX_DIR_DEPTH) workDirParents[workDirDepth++] = *curDir;
+    // Update workDirParents, workDirDepth, and workDir
+    if (update_cwd) {
+      if (workDirDepth < MAX_DIR_DEPTH) workDirParents[workDirDepth++] = *curDir;
+      workDir = *curDir;
+    }
 
-    // Point sub pointer to unused newDir
+    // Point sub at the other scratch object
     sub = (curDir != &newDir1) ? &newDir1 : &newDir2;
 
-    // item_name_adr point to next sub
+    // Next path atom address
     item_name_adr = name_end + 1;
   }
   return item_name_adr;

Marlin/src/sd/cardreader.h

   static inline uint8_t percentDone() { return (isFileOpen() && filesize) ? sdpos / ((filesize + 99) / 100) : 0; }
 
   // Helper for open and remove
-  static const char* diveToFile(SdFile*& curDir, const char * const path, const bool echo=false);
+  static const char* diveToFile(const bool update_cwd, SdFile*& curDir, const char * const path, const bool echo=false);
 
   #if ENABLED(SDCARD_SORT_ALPHA)
     static void presort();