Fix file browser not excluding AirDrop from the System list on macOS

There is already code for this, it just wasn't working. Now add the
slash after checking for an empty string.

Differential Revision: https://developer.blender.org/D6568

source/blender/editors/space_file/fsmenu.c

@@ -616,12 +616,12 @@ void fsmenu_read_system(struct FSMenu *fsmenu, int read_bookmarks)
           continue;
         }
 
-        /* Add end slash for consistency with other platforms */
-        BLI_add_slash(line);
-
         /* Exclude "all my files" as it makes no sense in blender fileselector */
         /* Exclude "airdrop" if wlan not active as it would show "" ) */
         if (!strstr(line, "myDocuments.cannedSearch") && (*line != '\0')) {
+          /* Add end slash for consistency with other platforms */
+          BLI_add_slash(line);
+
           fsmenu_insert_entry(
               fsmenu, FS_CATEGORY_SYSTEM_BOOKMARKS, line, NULL, ICON_FILE_FOLDER, FS_INSERT_LAST);
         }