shell: character clearing in the cursor up/down handler

[cy023]

Hi,

In shell.c, when the cursor up/down is entered, clear_prompt will be executed.

if (!__echo) {
  clear_prompt(count + 4);
} else {
  clear_prompt(count);
}

When __echo is off, count+4 characters are cleared, which will cause PROMPT to also be cleared.
I think only count characters need to be cleared. Are there any special considerations?

Thank you.