startup: default file selector to empty filename

Someone saved startup.blend w/ filename, tsk.

source/blender/blenloader/intern/versioning_defaults.c

@@ -131,6 +131,7 @@ void BLO_update_defaults_startup_blend(Main *bmain, const char *app_template)
 							const char *dir_default = BKE_appdir_folder_default();
 							if (dir_default) {
 								STRNCPY(sfile->params->dir, dir_default);
+								sfile->params->file[0] = '\0';
 							}
 						}
 						break;