correct truncated comment

Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

@@ -599,8 +599,8 @@
     if (parser.seen('S')) {     // Store (or Save) Current Mesh Data
       g29_storage_slot = parser.has_value() ? parser.value_int() : storage_slot;
 
-      if (g29_storage_slot == -1)                     // Special case, we are going to 'Export' the mesh to the
+      if (g29_storage_slot == -1)                     // Special case, the user wants to 'Export' the mesh to the
-        return report_current_mesh();
+        return report_current_mesh();                 // host program to be saved on the user's computer
 
       int16_t a = settings.calc_num_meshes();