🩹 Handle nullptr in CardReader::printLongPath (#23197)

Marlin/src/sd/cardreader.cpp

   //
   void CardReader::printLongPath(char * const path) {
 
-    int i, pathLen = strlen(path);
+    int i, pathLen = path ? strlen(path) : 0;
 
     // SERIAL_ECHOPGM("Full Path: "); SERIAL_ECHOLN(path);