cli: Correct handling of invalid escape sequences in cread_line()

cli: Correct handling of invalid escape sequences in cread_line()

The second call to cli_ch_process() is in the wrong place, meaning that
the one of the characters of an invalid escape sequence is swallowed
instead of being returned.

Fix the bug and add a test to cover this.

This behaviour matches that of the code before cli_getch() was
introduced. This was verified on the commit before b08e9d4b66 i.e.:

   7d850f85aad ("sandbox: Enable mmc command and legacy images")

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>