set cursor coord when not updating prompt contents

Sometimes offset can be -1, while it is also true that screen contents
have changed.  Example keystrokes: f<Down>, which enters the file-finder,
moves the tig cursor, and leaves the terminal cursor out of place.

src/prompt.c

@@ -49,6 +49,8 @@ prompt_input(const char *prompt, struct input *input)
 		last_buf_length = buf_length;
 		if (offset >= 0)
 			update_status("%s%.*s", prompt, pos, input->buf);
+		else
+			wmove(status_win, 0, buf_length);
 
 		if (get_input(offset, &key) == OK) {
 			int len = strlen(key.data.bytes);