When the eshell prompt is protected (e.g., with rear non-sticky,
inhibited movements, etc.), 'beginning-of-line' won't move to the
actual beginning of the line and therefore won't skip over the
prompt.
* lisp/eshell/em-prompt.el (eshell-previous-prompt): Use
'forward-line' to go to the beginning of the line, even if it's
protected. (Bug#39627)