man_generator: release buffer after use

Although ATM this code has no memory management at all,
it will not make any harm to release some memory,
when it's not needed anymore.

tools/command.c

@@ -2279,6 +2279,7 @@ static void print_val_man(struct command_name *cname, int opt_enum, int val_enum
 			else
 				printf("\\fB%s\\fP", line_argv[i]);
 		}
+		dm_free(line);
 		return;
 	}