Fix clearing with ctrl+k and ctrl+enter

zig/sdl/hello_sdl.zig

                            msg[pos] = '_';
                        },
                        c.SDLK_RETURN => {
                            result = runCommand(&msg);
                            result = runCommand(&msg, gpa);
                            var i: usize = 0;
                            while (i < max_chars) : (i += 1) {
                                msg[i] = ' ';
                            }
                            msg[max_chars] = 0;
                            pos = 0;
                        },
                        else => {},
                    }
                                    msg[i] = ' ';
                                }
                                msg[max_chars] = 0;
                                pos = 0;
                            },
                            else => {},
                        }